Greg Toppo has a thorough piece in USA Today about school lunches. Long story short: They're disgusting. A little competition in this arena would do a body good, but the politics (yes, messing with the school lunch program is political) are such that allowing schools to do the smart thing--i.e., find local purveyors to supply their cafeterias with decent food--isn't currently feasible.
Plus, as long as students are responsible for paying only about a dollar or two of their daily lunch costs, they're going to eat preprocessed garbage.