Can school's move down a class if there are bigger schools in the class below them?

[John]

I have noticed that, with the success factor not the issue, that some schools are competing at levels when they are actually bigger than schools in the class above them.  I noticed this with churubusco competing in 1a when they are bigger than some of the smaller schools in 2a.  I am just wondering are the classes by enrollment or can a school that has had a decline in enrollment drop down a class.