Good communication skills are essential for effective social work practice, yet evidence-based communication approaches are rarely applied in child and family social work. Motivational interviewing (MI) has shown promise in enhancing practitioners’ skills and outcomes in child and family social work, but its use outside the UK remains understudied. This study evaluates improvements in social workers’ communication skills following MI training tailored to child and family social work in Finland. The training included coaching sessions and a self-practice programme informed by behaviour change science. Thirty-three Finnish social workers participated. Recordings of simulated and real service user meetings were analysed using the Social Work and Interviewing Motivationally (SWIM) coding tool. Of the seven measured communication skills, only empathy showed statistically significant improvement at the group level. Due to the small sample size, statistical power was limited. Notably, person-based analyses identified three subgroups: nine participants improved, four declined, and the rest showed mixed changes. Exploratory survey analyses suggested that differences in practice, self-efficacy, and intentions influenced outcomes. These findings underscore the need to move beyond group averages to examine individual responses to training. Such detailed analyses can help optimize interventions and improve the effectiveness of communication skill development in social work.