The Finnish educational system and curricula lay emphasis on play, collaboration and equality. Modern educational practices allow the learning environment to be enlarged from indoor classrooms to outdoor playful learning environments (PLEs). PLEs have been constructed in schoolyards in Finland with the goal of increasing learning through play in curriculum-based education and augmenting collaborative play (ColPlay) between boys and girls. In order to better understand and describe such developments, the author set out to ascertain how teachers perceive mixed-gender play activities in pre-primary and basic education. Fourteen teachers were interviewed and the obtained data were analysed using the grounded theory as an analytical approach. The research suggests five premises for ColPlay: (1) the most suitable forms of ColPlay are outdoor games and role-play, (2) gender roles adjust in contemporary play culture, (3) teachers' pedagogical thinking on ColPlay includes various practices to promote collaborative relationships between girls and boys, (4) teachers have confidence in ColPlay and (5) learning to collaborate with both genders requires practice and reflection. The study offers useful insights for teachers, teacher educators and designers of game content and learning environments. (Contains 1 figure.)