Intersession is what they call the "extra" breaks that are not on the calendar for schools that are not "year round." Intersessional days are the days they offer the "Camps" which are usually project based, block scheduled, fun hands-on learning opportunities. Teachers have to interview to do it and get paid extra for working them. It's much more fun to teach intersessional days. There are smaller classes. The kids that are there want to be there. There is no grading necessary, no tests, no scope and sequence to follow. I always worked teaching summer school when I was a teacher. I would much prefer the year round (or level calendar) and teaching intersessional classes to State Standardized Testing Remediation.