Based on a classroom study conducted in a Swedish Grade 3, this presentationexplores students’ participation in mathematics. Video-recorded observationswere analyzed based on two theoretical approaches connected to teachers’pedagogical and subject matter knowledge, and relational abilities. Instances,where the two theoretical approaches intersected, were analyzed focusing onstudents’ participation in mathematics framed by a social practice theory. Thetentative results show that when the teacher in interaction with the students,uses both her mathematical knowledge for teaching and her relational abilities,the students sustainably participates in solving an open number sentence.