Though I know much of IM's research is based on training 5 days a week, my experience has led me to recommend 3 or 4 days a week when school is in session, especially for children with lower stamina. If students do 5 sessions a week during the school year, I find that on Friday I usually don’t see the gains that I do the other days. The combination of school and IM is just too exhausting!
During the summer, I do IM five days a week. No problem. When I am in a school, I also do IM 5 days a week. The teachers have helped to work out the schedules so the children won't have much make up homework and the children miss less class time with no travel time. I do notice some children in the schools are a little less efficient by Friday, but I don't have the flexibility to stretch the training out like I do in my office. I typically see very nice gains either way - 3 days a week or 5 days a week.