In many countries, sex equality is an essential aim of physical education (PE) curricula, while the PE grouping practices are widely hetero-normative. As far as there is a discrepancy between the curricula and practice, equality will not fully take place. This study examined the associations between PE teachers' perceived teaching efficacy (student engagement, instruction, class management) and preferences for single-sex (i.e. juridical sex) vs. coeducational grouping in PE. The analysis, based on a cross-sectional online survey of 175 Finnish PE teachers, showed that higher perceived class management was associated with the stronger preferences for single-sex PE. Associations of teacher's age and teaching experience with the preferences for coeducational vs. single-sex PE showed considerable heterogeneity. PE teachers' teaching efficacy, especially in class management, for teaching diverse groupings of students could be improved through in-service teacher training in accordance with the national curriculum.