The Moving Maths study was conducted to increase third grade pupils' physical activity and support their learning in Finland. Altogether 397 children (mean age 9.3 years) and 22 teachers took part in an intervention with two types of physically active maths lessons for five months. One group carried out lessons in which PA was integrated into maths learning goals, while another group implemented PA as short breaks. A control group was also allocated. The aim of the current study was to qualitatively examine classroom teachers' (n = 12) experiences and perceptions of student engagement during the intervention. The results indicated that pupils showed positive emotional and social engagement in both intervention groups. Positive cognitive engagement was indicated by concentration on seated work after the activities, but some teachers reported uncertainty about the learning results. It is concluded that in addition to reducing children's harmful sedentary behaviour, physically active lessons can positively affect student engagement and may thus enhance learning.