While getting stuff ready for the soon-to-be-here school year, I came across Joe Lancaster and the Monitorial system, where older students who have mastered certain content areas are charged with teaching the younger students. In one form or another, the monitorial system is at work at university level, for example TA's and Lab Instructors. However, at the secondary level I have not seen much, if any, evidence of the monitorial system. I know that some schools have "student interns" that typically just take care of administrative stuff such as grading or handing out paper. I am more wondering about older students actually taking over and teaching younger students. Has anyone had an encounter with this at a secondary level? Has it been effective?