Just because gubmint stops doing something doesn't naturally mean that the world will come to an end for the less affluent.
Who says that the poor communities wouldn't have their own pay-as-you-go schools?
Who says there wouldn't be national franchises, like maybe Wal-Mart or Target, that would have low prices as their chief selling point?
Your non concern for the lower class makes me believe you are fairly well off yourself. How right am I?
"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."
I don't believe the general welfare point would be covered very well by a cycle of poverty. Sure, it would be nice if you didn't have to waste your tax dollars on student who fail out anyways, but it is the best interest of the general population of the country to have public schools.