Using language for social purposes can be a real challenge for children with autism spectrum disorder (ASD) and developmental language disorder (DLD). Despite the positive effects of the Pragmatic Intervention Programme (PICP) already known in both populations, the effects needed to be established with a larger sample and analysed separately for each condition. This study aims to analyse the effectiveness of PICP on preschool-age children with ASD or DLD with pragmatic impairment. A non-randomised controlled trial was conducted. Thirty-six children were assigned to experimental (n = 22) or control group (waiting list) (n = 14). Each child attended 24 PICP-based intervention sessions provided by a speech and language therapist. The primary outcome measure was a Goal Attainment Scale (GAS). The secondary outcomes were "Escala de Avaliação de Competências Comunicativas" (EAC) and "Teste de Linguagem -- Avaliação da Linguagem Pré-Escolar" (TL-ALPE). The results indicated that all children achieved clinically significant progress in GAS after intervention. Statistically significant differences were observed between the experimental and control groups in the EAC and TL-ALPE after post-intervention assessment (T2). These results reinforce that PICP improves language in preschool-age children with ASD and DLD with pragmatic impairment. Differences between conditions and implications for future studies are discussed.