Abstract
Exploring the individual differences of the longitudinal growth of early numeracy (EN) in young children with Intellectual disabilities (IDs) prerequires the critical stage of exploring and validating the potential factor structure. Despite the fact that Relational Skills (RS), Counting Skills (CS) and Operations (O) are expected to constitute distinct domains of EN, there is not sufficient evidence to support either the above position or the position that they are different means of assessing a general-informal numeracy skill construct. This study was designed to shed light in the field through the evaluation of a measurement model describing the structure of RS, CS and O domains of EN and their interrelation. The sample included N = 155 children with IDs, enrolled in special school classes, mentally aged between 5;02 (y;m) and 6;10 (M = 5.11, SD = 0.974). Confirmatory Factor Analysis indicated a "good fit" of the two-factor model (RS, CS + O) of EN in ID (RMSEA=.029 < 0.08, CFI = 0.98 ≥ 0.90 and SRMR = 0.000 < 0.08). No measurement invariance across gender was reported for the proposed two-factor model of EN. The nested EN models validated full measurement invariance across gender. Finally, educational implications are discussed.