This study explores how brief in-service training influences preschool teachers' awareness of competences relevant for building high-quality teacher-child relationships. A pre- and post-test design was used, with a 5-h training session in-between. Thirty-four in-service preschool teachers completed a video-based task before and after training. Qualitative and quantitative analyses were conducted. After the session, the number of teachers identifying the key principles of building relationships with children was significantly higher for one out of the five situations analysed; the number of teachers identifying competencies for building positive relationships was significantly higher for three out of the five situations. Strategies such as observing children were easily identified (before and after training) and strategies such as taking into account the child relational needs were hardly ever identified (before and after training). Discussion highlights potential differential effects of brief in-service training according to the complexity of the training content.