This study evaluated the efficacy of preschool Promoting Alternative Thinking Strategies (PATHS), an early years curriculum designed to improve children's social and emotional competence, and reduce problem behaviour. Fifty-seven children aged three to four years took part in the study over one academic year. The control group (Group 1) received no preschool PATHS curriculum, Group 2 received an adapted version, and Group 3 received the full preschool PATHS curriculum. Relevant vocabulary and perspective-taking skills were assessed before and after the intervention alongside behavioural questionnaires completed by preschool staff and parents. Staff views were investigated. Group 3 significantly improved on some measures, but Groups 1 and 2 showed no significant improvements. Children who received the full version of the preschool PATHS curriculum exhibited less problem behaviour, showed better emotional knowledge, better attentional skills, and better prosocial behaviour. The contribution of the local Educational Psychology Service to the initiative is discussed.