47% of households do not pay Federal income taxes [1] and about 10% of households pay no net Federal Taxes whatsoever [2]. Their contribution might be in the form of State or municipal taxes (which don't exist in all states/cities) or through local sales taxes. The poor contribute minimally to funding public education.

EDIT: I have some more fact finding to do. The proportions of public education funding are 47% state, 44% local, 10% federal [3] so the amount paid by those under the poverty line depend greatly on the tax structure where they live.

EDIT 2: I can't find any good comprehensive state and local studies on education funded by taxes from the poor. I'll have to concede the point until I can find more proof. Theoretically you would expect the poor to contribute less to education because they pay less in taxes but I can't find the appropriate statistics to prove that.