The obvious question is.... is there a good population of larger crappie in the lake you are fishing. There are a lot of lakes which dont produce a good population of larger crappies. This can be do to stunting and or lack of food for the crappie.
To answer your question, yes, crappie do often school by size. Often you can catch a raogue fish tht may be a curve breaker, but the general rule is they school by size.
Crappie schools will often move around a lot, expecially at trasition times of the day. IE, light to dark and vise versa. If you are getting smaller fish at one time of the day, check it again at a different time of the day. The fish are there for a reason, most likely food.
The larger schools of crappie will often suspend over the deepest part of the lake, if your lake has unusually deep holes, they will search out area of the lake that may be shallower yet still has a deep hole.
I often find the best spots to be saddle areas between two points or a point and sunken island.