I read an interesting article on bilingual education, which focused on California. "The Bilingual Ban That Worked" gives a pretty good history of the evolution of California's bilingual education and explores how to determine what has worked.
Hispanic test scores on a range of subjects have risen since Prop. 227 became law. But while the curtailment of California's bilingual-education industry has removed a significant barrier to Hispanic assimilation, the persistence of a Hispanic academic underclass suggests the need for further reform.