From an article on the government and the non-profit sector in the Winter, 2011 issue of National Affairs:
The conclusion of a January 2010 report by the federal Department of Health and Human Services-titled Head Start Impact Study--that compared Head Start participants of a contrl group. The study found that virtually all gains in vocabulary, math, and other skills realized by Head Start children had dissipated by the time the students completed the first grade. To Isabel Sawhill of the Brookings Institution and Jon Baron of the Coalition for Evidence-Based Policy, the report demostrated that the program "had almost no effect on children's cognitive, social-emotional, or health outcomes at the end of 1st grade."
According to the same article, by Howard Husock, Head Start receives $7 billon per year. Perhaps we would save a bit less than that by shutting it down, as we would have to pay unempoyment for the people who are employed by the program. It might also be wise to use another chunk of that money to look for more effective ways to improve education. So let's call it $6.5 billion per year.