Educational reforms worldwide have resulted in schools increasingly incorporating open and flexible classroom designs. Open learning spaces may contribute to a student’s behavioral and emotional school engagement directly and by facilitating classroom-based physical activity (CPA). We investigated the associations between accelerometer-assessed CPA and student ratings of task-focused behavior and attitude towards school as indicators for behavioral and emotional engagement, respectively, with the associations of gender, grade, and classroom design on CPA among 206 3rd and 5th grade students in open learning spaces and conventional classrooms. Structural equation modelling showed open classroom design to be directly associated with better attitude towards school (B = −0.336; CI95% −0.616 to −0.055), but not with task-focused behavior. The relationship between task-focused behavior and attitude towards school was statistically significant (B = 0.188; 95%CI 0.068 to 0.031). CPA was not associated with task-focused behavior and attitude towards school, while classroom design (B = 1.818; 95%CI 1.101 to 2.536), gender (B = 1.732; 95%CI 20 1.065 to 2.398), and grade (B = 1.560; 95%CI 0.893 to 2.227) were statistically significantly associated with CPA. Open learning spaces seem to be associated with better emotional engagement, which is associated with behavioral engagement. Longitudinal studies investigating associations of open learning spaces and CPA on students’ behavioral, emotional, and cognitive engagement concurrently are warranted.