The purpose of this study is to gain knowledge about conditions for boundary crossing between academic and vocational practices and to identify dimensions of social practice within workplaces. The data consist of 28 questionnaires and 14 in-depth interviews with newly qualified secondary school teachers in their first year of teaching. We use the lens of sociocultural theory to analyse qualitatively what we can learn from newcomers' talk about their experiences and whether theories provided during their teacher education helped them to meet challenges in their new workplaces. Theoretically, notions of participation in social practices in terms of social space are in focus. In the findings, such space is identified as social adjustment, social distance, social inclusion and social expansion. Drawing on these concepts, we suggest that professional development depends strongly on the way new teachers' boundary crossing is supported by collaboration and to what extent they belong to professional dialogues in settings with inclusive and expansive relationships. (Contains 1 table and 1 note.)