Ditto what PP said. Schools are given an allocation for classroom teachers based on enrollment, whether the school is over capacity or not. "Over crowded" schools will have more portables. Title I schools (high rate of students eligible for free/reduced meals) have a smaller class size, so you will generally see 15-18 in kindergarten. Non-Title I schools will probably have 25-28. If you're interested in a particular school in MCPS, you can check out the "at a glance" web page to see details about enrollment/capacity, as well as average class size for K, Grades 1-3 and Grades 4-5.

Overcrowded means that the school is over capacity.

For example, look at Little Bennett ES in Clarksburg: http://www.montgomeryschoolsmd.org/departments/regulatoryaccountability/glance/currentyear/schools/02336.pdf

On the first page, you see that enrollment in 2012-2013 was 957. On the second page, you see that the capacity of the school is 673.

"Overcrowded" has nothing to do with class size.

When posters say a school is overcrowded, what do they mean in terms of class size? What is the average class size you are looking for in kindergarten and elementary years?