Just Coincidence?

I was in a top-rated school today and enjoyed the students.  But, there is one thing that seems a bit odd.  I have been ranting about large class sizes in most schools.  This class was only 22 students.  That is the smallest class I have had for a long time.  It could be just a fluke of numbers and classes, but it seems odd that a top-rated school would have a smaller class and the struggling schools have much larger classes.