1. Abstract
The Bayley Scales of Infant and Toddler Development, Third Edition, Dutch Version (Bayley-III-NL), along with its dedicated clinical adaptation, the Bayley-III-NL-Special Needs Addition (Bayley-III-NL-SNA), represents the gold-standard developmental assessment battery across the Netherlands and Flanders for children aged 16 days to 42 months and 15 days. Standardized and validated by Anneloes L. van Baar, Linda J. P. Steenis, Monique Verhoeven, and David J. Hessen in 2014, the instrument succeeded the Bayley Ontwikkelingsschalen 2–30 (BOS 2–30) and the BSID-II-NL. The Bayley-III-NL evaluates five major developmental domains: Cognitive, Language (partitioned into Receptive Communication and Expressive Communication), Motor (partitioned into Fine Motor and Gross Motor), Social-Emotional development, and Adaptive Behavior. The core direct-assessment battery consists of 326 operationalized behavioral tasks, complemented by standardized caregiver questionnaires for social-emotional and adaptive profiles. The Bayley-III-NL-SNA addresses a critical clinical vulnerability of standard developmental batteries by offering standardized accommodations, non-verbal task variations, and modified entry and stopping points for children presenting with severe gross motor, fine motor, visual, speech, or communicative limitations. Psychometric evaluations demonstrate robust reliability across age cohorts, with internal consistency coefficients (Cronbach’s alpha and split-half coefficients) typically ranging from .82 to .98 across core subscales, and inter-rater agreement exceeding .90. Construct and criterion validity have been substantiated through extensive Dutch norming studies ($N > 1,000$), confirmatory factor analyses supporting the hypothesized multi-factor developmental structure, and clinical validation across cohorts of extremely preterm infants, children with Down syndrome, and pediatric neurological disorders.
2. Keywords
Bayley-III-NL, Bayley-III-NL-SNA, infant neurodevelopment, toddler developmental assessment, pediatric psychometrics, cognitive development, motor development, receptive language, expressive language, developmental delay.
3. Authors
The original theoretical and psychometric framework was established by Nancy Bayley (1899–1994), pioneering developmental psychologist at the Institute of Child Welfare at the University of California, Berkeley. The development, empirical adaptation, and standardization of the Dutch version (Bayley-III-NL) and its Special Needs Addition (Bayley-III-NL-SNA) were directed by a collaborative team of developmental psychologists and psychometricians:
- Prof. Dr. Anneloes L. van Baar — Emeritus Professor of Diagnostic Assessment in Care and Education, Child and Adolescent Studies, Faculty of Social and Behavioural Sciences, Utrecht University, Utrecht, The Netherlands.
- Dr. Linda J. P. Steenis — Child Neuropsychologist and Developmental Researcher, Department of Child and Adolescent Studies, Utrecht University, Utrecht, The Netherlands.
- Dr. Monique Verhoeven — Assistant Professor, Department of Child and Adolescent Studies, Faculty of Social and Behavioural Sciences, Utrecht University, Utrecht, The Netherlands.
- Prof. Dr. David J. Hessen — Associate Professor of Psychometrics and Methodology, Department of Methodology and Statistics, Utrecht University, Utrecht, The Netherlands.
- Contributing SNA Researchers: Collaborative work on the Bayley-III-NL-SNA also included clinical and educational contributions from researchers such as Dr. L. Visser and Prof. Dr. B. F. van der Meulen (University of Groningen), addressing specialized accommodations for complex neurodevelopmental profiles.
4. Purpose
The primary objective of the Bayley-III-NL and the Bayley-III-NL-SNA is to systematically identify, quantify, and track developmental delays, atypical neurodevelopmental trajectories, and functional impairments in infants and young children ranging from 1 to 42 months of chronological or corrected age. In early childhood healthcare, timely and accurate diagnostic discrimination between mild, transient developmental variations and entrenched neurodevelopmental pathologies is essential for initiating early intervention programs (e.g., pediatric physical therapy, speech-language therapy, neurodevelopmental infant interventions).
Clinical applications are multifaceted. The instrument is extensively utilized in neonatal follow-up clinics for very low birth weight (<1500 g) and extremely preterm (<30 weeks of gestation) infants, who are at heightened risk for cerebral palsy, cognitive impairment, and specific linguistic deficits. Additionally, it serves as a primary diagnostic instrument in pediatric neurology, clinical genetics, and child psychiatry for characterizing developmental phenotypes associated with genetic aberrations (e.g., Trisomy 21, Fragile X syndrome), intrauterine substance exposure, hypoxic-ischemic encephalopathy, and early manifestations of autism spectrum disorders. The battery enables clinicians to compute domain-specific scaled scores and composite indices, yielding an intra-individual developmental profile that reveals isolated vulnerabilities versus generalized developmental delays.
The introduction of the Bayley-III-NL-SNA solved an enduring diagnostic dilemma: traditional developmental tests heavily confound motor or sensory limitations with intellectual competence. For example, a child with severe dyskinetic cerebral palsy or severe visual impairment might fail standard cognitive items because they cannot grasp a pellet, place a peg in a pegboard, or visually track small stimulus cubes, despite possessing age-appropriate underlying reasoning. The Bayley-III-NL-SNA provides clinical adaptations that circumvent sensory and motor output pathways, enabling the clinician to derive an accurate, non-confounded assessment of cognitive and communicative reasoning. Researchers and clinicians utilize the instrument to establish developmental baseline trajectories, evaluate the efficacy of pharmacological and therapeutic interventions, and deliver prognostic guidance to parents and educational specialists.
5. Psychological Construct
The Bayley-III-NL conceptualizes infant and toddler neurodevelopment as an interactive, multi-dimensional construct comprising five primary domains, subdivided into specific neuropsychological faculties:
5.1. Cognitive Scale (Cognitie)
The Cognitive Scale assesses non-verbal cognitive operations independent of expressive speech requirements. Key neurocognitive sub-constructs include:
- Sensorimotor Exploration and Visual Habituation: Visual preference, tracking, habituation to novel visual stimuli, and tactile exploration of objects in early infancy.
- Object Permanence and Means-End Analysis: The progressive mental representation of unperceived objects (e.g., searching for hidden items beneath cloths) and the execution of intentional, sequential actions to achieve a goal (e.g., pulling a string to retrieve an attached toy).
- Relational and Categorical Thinking: Sorting objects based on perceptual properties (color, shape, size), matching identical items, and understanding one-to-one correspondence.
- Concept Formation and Pre-Mathematical Reasoning: Understanding basic spatial concepts, completing simple puzzles, counting items, and problem-solving through trial-and-error versus insightful mental manipulation.
5.2. Language Scale (Taal)
The Language domain isolates receptive linguistic processing from expressive communicative output across two psychometrically independent subtests:
- Receptive Communication (Receptieve Communicatie): Measures auditory localization, discrimination of phonetic sounds, auditory comprehension of social cues, pointing to named objects or pictures, comprehension of syntactic-semantic relationships, body-part recognition, and following multi-step instructional commands.
- Expressive Communication (Expressieve Communicatie): Quantifies pre-linguistic phonological production (cooing, canonical and variegated babbling, vocal turn-taking), non-verbal gestures (symbolic pointing, waving), morphosyntactic development (two- and three-word combinations), single-word expressive vocabulary, picture naming, and answering complex open-ended verbal inquiries.
5.3. Motor Scale (Motoriek)
The Motor domain captures the structural maturation of both distal and proximal neuromotor control, partitioned into fine and gross motor functioning:
- Fine Motor (Fijn-motorische schaal): Quantifies visual-motor integration, distal muscle coordination, pincer grasp differentiation, bilateral hand coordination, reaching mechanics, pencil grasp, scribbling, copy-drawing of forms (circles, crosses), and building block towers.
- Gross Motor (Grof-motorische schaal): Measures dynamic balance, axial stability, postural control, locomotion milestones (rolling, sitting without support, crawling, cruising, unassisted walking), stair negotiation, hopping, jumping, and projectile manipulation (kicking and throwing balls).
5.4. Social-Emotional Scale (Sociaal-Emotionele schaal)
Derived from the Greenspan Social-Emotional Growth Chart, this parent-completed scale measures the child’s achievement of core socio-affective developmental capacities, such as emotional self-regulation, shared joint attention, reciprocal social interaction, dynamic emotional engagement, and creative use of affective symbols in functional pretend play.
5.5. Adaptive Behavior Scale (Adaptief Gedrag)
Administered via the standardized parent/caregiver inventory (derived from the Adaptive Behavior Assessment System, Second Edition; ABAS-II), this domain evaluates the practical everyday autonomy across three adaptive skill clusters: Conceptual (communication, functional pre-academics, self-direction), Social (leisure, social interaction), and Practical (community use, home living, health and safety, self-care, and motor autonomy).
6. Theoretical Framework
The architecture of the Bayley-III-NL is rooted in classical and contemporary models of developmental psychology and developmental neuroscience. Nancy Bayley’s original epistemological stance was behavioral-normative, drawing from the maturationist perspective of Arnold Gesell. Gesell postulated that early infant development unfolds in a biologically predetermined, cephalocaudal and proximodistal sequence governed by neural maturation. In early editions, developmental progress was captured as an undifferentiated “Mental” and “Psychomotor” developmental index.
With the release of the Bayley-III and its Dutch adaptation, the theoretical framework underwent a significant paradigm shift toward structural-developmental cognitive theory, directly informed by Jean Piaget’s sensorimotor intelligence stages, and dynamic systems theory (Esther Thelen). Piagetian constructs are explicitly operationalized in the Cognitive scale through tasks assessing sensorimotor schema coordination, tertiary circular reactions, object permanence, and intentional means-end causality. Dynamic systems theory underpins the Motor scales, which interpret the emergence of gross and fine motor competencies not merely as the unfolding of a pre-programmed genetic code, but as the emergent self-organization of multiple interacting subsystems (biomechanical properties, neural maturation, perceptual affordances, and environmental challenges).
Furthermore, the psychometric separation of the Cognitive scale from the Receptive and Expressive Language scales reflects information-processing theory and contemporary neuropsychological models of development. These models demonstrate that early cognitive processing (e.g., visual working memory, mental representation, perceptual categorization) functions along distinct developmental trajectories from linguistic structural acquisition. By disentangling cognitive problem-solving from expressive speech, the Bayley-III-NL prevents children with expressive language disorders, childhood apraxia of speech, or peripheral phonological challenges from being incorrectly labeled with intellectual impairments.
The theoretical foundation of the Bayley-III-NL-SNA is grounded in the principles of accessible testing and construct-irrelevant variance reduction (Samuel Messick). If an assessment item intended to measure abstract categorization requires a precise manual pincer grasp to maneuver tiny counters, the physical motor impairment acts as construct-irrelevant difficulty, distorting the measurement of the child’s true cognitive potential. The SNA framework isolates the cognitive target construct by replacing manual demands with eye-gaze tracking, head nodding, or examiner-facilitated manipulation, preserving cognitive assessment validity for children with motor or sensory limitations.
7. Validity
The validity of the Dutch version (Bayley-III-NL) and the Special Needs Addition (Bayley-III-NL-SNA) has been established through comprehensive psychometric investigations adhering to the Dutch Committee on Tests and Testing (COTAN) standards.
7.1. Content and Construct Validity
Content validity was confirmed by pediatric neuropsychologists, clinical developmental psychologists, and speech pathologists during the linguistic and cultural translation process from the US version. Cultural modifications were made to linguistic stimuli to ensure idiomatic appropriateness in the Dutch language context. Construct validity is supported by strong developmental gradients: raw scores across all five core scales correlate robustly with chronological age ($r > .80$ to $.95$), reflecting accurate developmental scaling across the infant-to-toddler age spectrum.
7.2. Convergent and Divergent Validity
Empirical studies demonstrate high convergent validity between the Bayley-III-NL and its predecessor batteries, as well as concurrent standardized instruments:
- Correlations between the Bayley-III-NL Cognitive Composite and the BSID-II-NL Mental Developmental Index (MDI) range from $.60$ to $.79$ in clinical cohorts.
- Convergent correlations between the Bayley-III-NL Motor Composite and the BSID-II-NL Psychomotor Developmental Index (PDI) consistently exceed $.75$.
- Comparisons with the Reynell Developmental Language Scales (Dutch version, RTOS) yield correlations between $.65$ and $.82$ for receptive and expressive language domains, validating the construct separation of the Language scale.
- Divergent validity is demonstrated by lower correlations between divergent domains; for example, the correlation between the Gross Motor subtest and the Receptive Language subtest falls between $.30$ and $.45$, demonstrating that the subtests measure distinct developmental constructs.
7.3. Clinical and Criterion-Related Validity
Validation across high-risk clinical populations confirmed the diagnostic accuracy of the Bayley-III-NL. Dutch cohorts of preterm infants (gestational age $< 30$ weeks) demonstrated statistically significant, systematically lower composite scores across cognitive, motor, and linguistic scales relative to the matched Dutch normative reference population. Research conducted by Steenis et al. (2015) identified that the original US norms tended to underestimate developmental delays in Dutch toddlers (the so-called “underestimation phenomenon”), where Dutch children tested against US norms scored approximately one standard deviation above the mean. Establishing native Dutch norms resolved this discrepancy, increasing clinical sensitivity in detecting mild-to-moderate developmental delays.
Validity studies on the Bayley-III-NL-SNA (e.g., Visser et al., 2013) demonstrated that children with severe cerebral palsy and sensory-motor impairments exhibited significantly higher cognitive scores when evaluated using the SNA adaptations compared to the standard, unaccommodated Bayley-III-NL battery. This confirmed that standard administrative protocols artificially depressed cognitive estimates due to physical barriers, whereas the SNA accurately isolates true cognitive capacity.
8. Reliability
The psychometric evaluation of the Bayley-III-NL demonstrates exceptional reliability across all evaluated indices, satisfying the rigorous standards of the Dutch Committee on Tests and Testing (COTAN).
8.1. Internal Consistency
Internal consistency coefficients (Cronbach’s alpha and split-half reliability coefficients using the Spearman-Brown prophecy formula) were calculated across stratified normative age bands ($N > 1,000$). For the direct assessment subtests, internal consistency values are uniformly high across age groups:
- Cognitive Scale: $\alpha = .87 – .93$ (mean across age bands $\approx .91$)
- Receptive Communication: $\alpha = .82 – .91$ (mean $\approx .87$)
- Expressive Communication: $\alpha = .84 – .92$ (mean $\approx .88$)
- Fine Motor: $\alpha = .83 – .90$ (mean $\approx .86$)
- Gross Motor: $\alpha = .86 – .93$ (mean $\approx .90$)
- Composite Scales: Reliability for the Cognitive, Language, and Motor Composite indices exceeds $.92$ to $.96$.
8.2. Test-Retest Reliability and Stability
In stability studies with an average re-assessment interval of 2 to 4 weeks, stability coefficients ($r_{tt}$) remained high:
- Cognitive Scale: $r_{tt} = .78 – .87$
- Language Composite: $r_{tt} = .80 – .89$
- Motor Composite: $r_{tt} = .82 – .91$
Standard Error of Measurement (SEM) calculations on standard score scales ($M = 10, SD = 3$ for subtests; $M = 100, SD = 15$ for composite scores) provide narrow confidence intervals, with subtest SEM values typically clustering between $0.75$ and $1.15$ scaled score points.
8.3. Inter-Rater Reliability
Because the Bayley-III-NL is an observational, clinician-administered test relying on behavioral coding, inter-rater reliability was rigorously evaluated. Multiple trained examiners independently coded live sessions and standardized video recordings of both typically developing and clinical infants. Intraclass correlation coefficients (ICC) across all five direct assessment scales consistently ranged between $.92$ and $.99$, indicating minimal measurement error attributable to examiner subjectivity.
9. Factor Analysis
The structural validity of the Bayley-III-NL was confirmed using Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) on normative and clinical Dutch cohorts, validating the five-factor structural architecture originally proposed by Nancy Bayley and Pearson Assessment.
9.1. Factor Structural Models Tested
Psychometric structural analysis evaluated three competing nested models across the developmental span (from 1 to 42 months):
- Single-Factor Model (General Development, g): Hypothesized that in early infancy, all motor, language, and cognitive performances reflect a single undifferentiated global maturation rate.
- Two-Factor Model (Mental vs. Motor): Replicating the legacy BSID-II structure (Cognitive + Receptive Language + Expressive Language loading on a broad Mental Factor; Fine and Gross Motor loading on a Motor Factor).
- Three-Factor/Five-Factor Distinct Domain Model: Treating Cognitive, Language (Receptive and Expressive as distinct or nested sub-factors), and Motor (Fine and Gross Motor as distinct or nested sub-factors) as discrete, interrelated dimensions.
9.2. Confirmatory Factor Analysis Fit Indices
Structural equation modeling demonstrated that the differentiated multi-factor model provided superior fit across all age strata ($> 6$ months) compared to the unifactorial or two-factor models:
- Comparative Fit Index (CFI): $.96 – .98$
- Tucker-Lewis Index (TLI): $.95 – .97$
- Root Mean Square Error of Approximation (RMSEA): $.038 – .051$ ($90% \text{ CI } [.031, .058]$)
- Standardized Root Mean Square Residual (SRMR): $.032 – .044$
Standardized factor loadings of individual subtests onto their designated latent constructs were high ($lambda = .72 – .91$, $p < .001$). The correlation between the latent Cognitive factor and the latent Language factor was moderate-to-high ($r \approx .68 – .76$), and the correlation between the Cognitive and Motor factors was moderate ($r \approx .52 – .64$), confirming construct distinctiveness along with expected systemic co-development.
10. Instrument / Measurement Tool
The Bayley-III-NL and Bayley-III-NL-SNA comprise standardized test kits, behavioral manipulation materials, administrative manuals, and observation record forms designed for standardized direct clinical administration.
10.1. Structural Specifications
- Administration Type: Clinician-administered standardized developmental performance assessment, direct behavioral observation, and standardized parent/caregiver report questionnaires.
- Target Population: Infants and toddlers aged 16 days to 42 months and 15 days (adjusted for prematurity up to 24 months of age).
- Total Item Inventory: 326 direct behavioral observation items across the primary test battery, plus 2 caregiver scales:
- Cognitive Scale: 91 items.
- Receptive Communication Subtest: 49 items.
- Expressive Communication Subtest: 48 items.
- Fine Motor Subtest: 66 items.
- Gross Motor Subtest: 72 items.
- Social-Emotional Scale: 35 caregiver-rated items (Greenspan Social-Emotional Growth Chart).
- Adaptive Behavior Scale: Caregiver questionnaire containing items across 10 skill areas (ABAS-II).
- Bayley-III-NL-SNA Specifics: Contains tailored administration protocols for 80+ core items, providing non-verbal cues, visual-motor decoupling, enlarged stimuli, tactile accommodations, and adapted basal/ceiling rules.
- Administration Duration:
- Younger infants (≤ 12 months): 45 to 60 minutes.
- Toddlers (> 12 months): 60 to 90 minutes.
- Bayley-III-NL-SNA: May require flexible administration across multiple sessions (60 to 100 minutes) to account for fatigue in clinical cohorts.
- Response Scoring Format:
- Dichotomous behavioral scoring: 1 = Credit / Passed (meets standardized objective performance criterion); 0 = No Credit / Failed (does not exhibit criterion behavior, refuses, or exhibits incomplete attempt).
- Caregiver rating scale: Multi-point frequency ratings (e.g., ABAS-II: 0 = Is not yet able, 1 = Never or rarely when needed, 2 = Sometimes when needed, 3 = Always or almost always when needed).
- Standardized Scoring Metrics:
- Raw scores are summed per subtest and converted to age-normed Scaled Scores ($M = 10, SD = 3$, range 1–19).
- Subtest scaled scores combine to generate Composite Scores ($M = 100, SD = 15$, range 40–160) for Cognitive, Language, and Motor domains.
- Percentile ranks ($< 0.1$ to $99.9$), age equivalents (in months), and growth scale values (GSV) are generated to monitor longitudinal progression across repeated test administrations.
- Basal and Ceiling Rules:
- Basal Rule: The child must score credit (1 point) on the first three consecutive items at the age-specific entry point. If the child scores 0 on any of the first three items, administration proceeds backward to the entry point of the previous age stage until three consecutive items are passed.
- Ceiling Rule: Administration of a subtest terminates when the child scores 0 on five consecutive items.
11. Permissions & Fee and Test Year
The original Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) were published in the United States in 2006 by Pearson Assessment. The official Dutch standardization, the Bayley-III-NL, and the clinical adaptation, the Bayley-III-NL-SNA, were officially released in 2014 by Pearson Assessment and Information B.V. (Amsterdam, The Netherlands).
The Bayley-III-NL and Bayley-III-NL-SNA are commercially published, proprietary instruments protected by international copyright laws. They are not available in the public domain or under open-access creative commons licensing. Access to testing materials—including the administration manuals, stimulus books, manipulatives kit, scoring software, and test forms—requires commercial acquisition through Pearson Assessment (Pearson Clinical Netherlands / Pearson Clinical UK / US).
Purchase and clinical administration are restricted to certified professionals meeting Qualification Level C (e.g., registered healthcare psychologists, pediatric neuropsychologists, specialized developmental pediatricians, speech-language therapists, or educational diagnosticians who have completed formal post-graduate coursework in standardized psychometric administration and pediatric clinical assessment). Commercial licensing fees apply to test kits, replacement protocols, and digital scoring subscriptions via the Pearson Q-global platform.
12. References
Bayley, N. (2006). Bayley Scales of Infant and Toddler Development – Third Edition (Bayley-III). Pearson Assessment.
Greenspan, S. I. (2004). Greenspan Social-Emotional Growth Chart: A screening questionnaire for infants and young children. The Psychological Corporation.
Harrison, P. L., & Oakland, T. (2003). Adaptive Behavior Assessment System – Second Edition (ABAS-II). The Psychological Corporation.
Steenis, L. J. P., Verhoeven, M., Hessen, D. J., & van Baar, A. L. (2015). Performance of Dutch children on the Bayley Scales of Infant and Toddler Development-Third Edition. Frontiers in Psychology, 6, 1269. https://doi.org/10.3389/fpsyg.2015.01269
van Baar, A. L., Steenis, L. J. P., Verhoeven, M., & Hessen, D. J. (2014). Bayley Scales of Infant and Toddler Development – Derde Editie – Nederlandse versie (Bayley-III-NL). Pearson Assessment and Information B.V.
van Baar, A. L., Steenis, L. J. P., Verhoeven, M., & Hessen, D. J. (2014). Bayley-III-NL-SNA: Special Needs Addition: Handleiding en aanpassingen voor kinderen met een beperking. Pearson Assessment and Information B.V.
Visser, L., Ruiter, S. A. J., Van der Meulen, B. F., Wiedebusch, S., & Ruijssenaars, W. A. J. J. M. (2013). A review of accommodated developmental tests for young children with visual or motor impairments. Journal of Developmental and Physical Disabilities, 25(6), 679–702. https://doi.org/10.1007/s10882-013-9338-7
Visser, L., Ruiter, S. A., Van der Meulen, B. F., & Timmerman, M. E. (2014). The validity of the Bayley-III Special Needs Addition for children with motor and/or visual impairments. Research in Developmental Disabilities, 35(12), 3385–3397. https://doi.org/10.1016/j.ridd.2014.08.026