Population and Birth Rate (about school abandon)

I think  one reason of school abandon  might be population decrease and low birth rate. So I did some research on that. Here is what I found.

Geography	Cumulative Estimates of the Components of Population Change
	April 1, 2010 to July 1, 2012
	Total Population Change [1]	Natural Increase	Vital Events		Net Migration
			Births	Deaths	Total	International [2]	Domestic
Pennsylvania	61,157	37,311	320,606	283,295	26,819	54,466	-27,647

Geography	Annual Estimates of the Components of Population Change
	July 1, 2011 to July 1, 2012
	Total Population Change [1]	Natural Increase	Vital Events		Net Migration
			Births	Deaths	Total	International [2]	Domestic
Pennsylvania	19,588	13,996	141,011	127,015	6,291	25,058	-18,767

In these two charts， we can see in fact the population is growing and the raio of births to deaths is over 1. There seem to be no problem of demographics. However, I read a paper about population spatial layout of megalopolis in northeastern part of United States. The author says that in well-developed megalopolises like Philly ,the Pyramid structure is obvious for urban hierarchy, population increases happened in outer suburban district rather than suburban. I think this point is very interesting and might be the answer of our question. Maybe we can find more datas of this and discuss on class.