Résumé : To meet the requirements of the 21st century school, it would therefore seem necessary to rethink how mental health is organized and particularly within the physical learning environment. This has been done in Quebec, Canada, where ‘flexible’ seating allow students to choose where they sit and work during the day. Student-student and student-teacher exchanges also have an impact on the mental health of children in school. Indicators of mental health were studied among 107 students in three flexible seating group and three fixed seating group. Two models were created based on gender, and Student T-tests were used for two databases. Another database for teachers was analyzed descriptively by group. Girls in the flexible seating group had lower scores for internalizing problems, inattention/hyperactivity, school problems, and emotional symptoms compared to girls in the fixed seating group. For boys, there was a decrease in school problems alone and an increase in the other variables. For teachers, there was an upward trend in median scores in the flexible seating group. In general, classroom layout appears to have played a role in the students’ school mental health and a particularly beneficial role for girls. In practice teachers should consider that some of their students may not feel comfortable in a flexible layout. More support and help from the teacher to these students could help them to cope with the changes brought by flexible seating. Beyond the students’ comfort, for teachers, this would allow them to meet their students’ needs through differentiated instruction and differentiated learning.