Public schools are over-funded and the money spent on public schools does not correlate to the educations provided. Here is a graph showing test scores vs spending:
Spending is about $26,000 for each student signed up at a DC public school, and $28,000 for each student who actually attended. The cost of the average private school is only $6,620. So they cost a quarter of what public schools do, but still they do better.
If we imagine that supermarkets were run by the government in the same way that public schools are managed and funded today, the average monthly food cost for people choosing to shop at private supermarkets would be $550/month ($6,620/year), and public supermarkets would be spending $2,350 per month to feed its patrons, people being fed by public supermarkets would not have a choice about the foods they received, and the public markets would be providing rotten foods with little nutritional value (failing to teach people to read). Administrators of public markets would insist that the reason they cannot provide a variety of fresh and nutritious foods is that they lack funding, and about half of America would agree with them.