Recess improves 3rd graders classroom behavior--maybe

The What Works Clearinghouse provides an evaluation of a study which found that teachers report better classroom behavior when students have regular access to recess. WWC also cautions that the populations that have regular access to recess were different in several ways from the populations that didn't, and these differences may or may not have been corrected for by data analysis.

Barros, R. M., Silver, E. J., & Stein, R. E. K. (2009). School recess and group classroom behavior. Pediatrics, 123(2): 431–436.
(online access to this article is available through the UNLV Libraries)