University of Minnesota recently released a study that contradicts the commonly-held notion that serving healthier school meals will mean fewer students buy school lunch. According to an AP article Study: Kids Will Eat Healthy School Food , the study found that sales of school meals in Minnesota did not decline when healthier foods were served, and that healthier meals didn't have to cost more to produce.
Note: I have downloaded the journal article in pdf. Please let me know in comments or by email if you'd like more details.