Chronological Age and Adaptive Outcomes Following Neuropsychomotor and Aquatic Interventions in Children with Autism: A Secondary Analysis

Background: Autism Spectrum Disorder (ASD) can be conceptualized not as a static condition but as a dynamic disorder of developmental regulation, in which neuroplastic potential is translated into functional gains only through structured, experience-dependent therapeutic input. Neuropsychomotor Therapy of Early Development (TNPEE) and Therapy in Aquatic Motor Activities (TAMA) have shown differential efficacy in children with ASD, but whether chronological age moderates the magnitude of therapeutic response—or whether the characteristics of the intervention itself are the stronger determinant of outcome—has not been systematically examined. Methods: This was a non-randomized, exploratory secondary stratified analysis of a multicenter 18-month longitudinal cohort (N = 77 children with ASD, age 4–12 years) allocated to three groups: TAMA only, TNPEE combined with TAMA (TAMA+TNPEE), or TNPEE only. Participants were stratified into a younger (≤6 years, n = 16; TAMA n = 8, TAMA+TNPEE n = 3, TNPEE n = 5) and an older (>6 years, n = 61; TAMA n = 18, TAMA+TNPEE n = 22, TNPEE n = 21) subgroup. Adaptive functioning was assessed with the Vineland Adaptive Behavior Scales, Second Edition (VABS-II) at baseline and 18 months. Between-stratum comparisons used the Mann–Whitney U test; Spearman rank correlations and ANCOVA models with Age × Treatment interaction terms were used to test age moderation within a neuroplasticity-recruitment framework. Results: In the TAMA-only group, younger children showed significantly smaller adaptive gains than older children across the Composite (2.22 ± 1.14 vs. 3.53 ± 0.76, p = 0.012), Communication (p = 0.041), and Socialization (p = 0.016) subscales, with significant positive Spearman correlations between age and adaptive gains (r = 0.397–0.437). Simple slope analysis confirmed a significant age effect within the TAMA group (b = 0.231, SE = 0.083, p = 0.010) but not in the TNPEE (b = 0.133, p = 0.157) or TAMA+TNPEE (b = 0.135, p = 0.198) groups. The formal Age × Treatment interaction term in the ANCOVA did not reach statistical significance (all p > 0.18). As this interaction test is the formal statistical test of differential age moderation, the simple-slope pattern above should be regarded as exploratory rather than confirmatory. Treatment group accounted for the large majority of variance in adaptive gains (partial η2 = 0.78–0.95), whereas age explained only a small proportion of outcome variability. ASD severity level transitions were comparable across age strata in TNPEE-based groups. Conclusions: In this exploratory secondary analysis, TNPEE-based interventions were associated with adaptive gains that did not differ significantly by age across the 4–12 year age range, whereas aquatic therapy alone showed an age-dependent pattern favoring older children. These findings are hypothesis-generating and consistent with a neuroplasticity-recruitment model in which therapeutic architecture—rather than chronological age alone— may be associated with how effectively latent plastic potential is translated into developmental gains, although the non-significant Age × Treatment interaction and the small, imbalanced subgroups (including n = 3 in the youngest TAMA+TNPEE stratum) mean these findings require confirmation in adequately powered, prospectively designed studies, with implications for clinical decision-making regarding therapy timing and design.