BACKGROUND

Children with autism spectrum disorder (ASD) and children with development language disorder (DLD) often experience syntactic impairments. It is of the utmost importance to implement evidence-based intervention at the earliest possible stage to mitigate the adverse effects of these difficulties. Internationally, several programs are supported by scientific evidence. In Portugal, there are currently only two intervention programs, one of which is PROsyntax. However, its effectiveness has not yet been established.

AIM

This study aims to determine the effects of PROsyntax on expressive and receptive syntax in preschool-age children with syntactic impairments diagnosed with DLD or ASD.

METHODS AND PROCEDURES

This study is a nonrandomized controlled trial with a nonprobabilistic convenience sample. Thirty-one children aged between 3 and 6 years were recruited and allocated into an experimental group (EG, intervention group) ( = 14) and a control group (CG, without intervention) ( = 17). A blind pre- (T1) and postintervention (T2) assessment was conducted using two standardized instruments (SIN:TACS for expression and Subtest 3 of Avaliação da Linguagem Oral (ALO) for comprehension). Children in the EG received intervention with PROsyntax, comprising 24 sessions, biweekly, lasting 1 hr each. The intervention was conducted within the school setting by a speech and language therapist.

OUTCOMES AND RESULTS

Statistically significant improvements were observed in the EG compared to the CG in both expressive (F(1,27) = 293.22;  < .001; η  = 0.92) and receptive (F(1,27) = 147.18;  < .001; η  = 0.85) syntax. Large effect sizes were found (SIN:TACS: d = 4.07 (DLD) and d = 11.67 (ASD); ALO: d = 3.29 (DLD) and d = 4.31 (ASD)). Strong correlations between measures were observed at both time points. Postintervention, the CG also received the intervention and showed comparable gains. High satisfaction ratings were reported by both families and early childhood educators.

CONCLUSIONS AND IMPLICATIONS

The findings provide preliminary evidence supporting the effects of PROsyntax in improving expressive and receptive syntactic skills in preschool-age children with ASD or DLD. These findings have important implications for clinical practice, suggesting that explicit interventions can yield significant gains in preschool-age children with syntactic impairment. However, the nonrandomized design, small sample size, and absence of long-term follow-up limit the generalizability of results. Further research is needed to confirm these effects and explore differential responses across diagnostic groups.