The UK's Guardian newspaper just published an article reporting on the most cost-effective ways for schools to spend extra money. It turns out that effective feedback to students, peer tutoring, and parental involvement are more effective as well as more cost-effective than school uniforms, reducing class size, or performance pay. The article draws on a research report from the Sutton Trust.
The report itself is definitely worth a look, because it defines what it means by practices such as effective feedback, reducing class size, teaching assistants, summer school, homework, peer tutoring, ability grouping, and parental involvement. A chart shows the relative cost of the different interventions along with the expected student gain in months of increased learning per year of intervention. Then a separate sheet on each intervention discusses the nature and strength of the evidence. It looks a bit less rigorous but more general and perhaps more useful to help allocate resources than the new practice guides in our own What Works Clearinghouse.