The author reports findings from a federal study of 77 middle schools which suggest that even intensive, state-of-the-art efforts to boost teachers' skills on the job may not lead to significant gains in student achievement right away. The "Middle School Mathematics Professional Development Impact Study," which was released in April, is the second major experimental study by the U.S. Department of Education's Institute of Education Sciences to find that a high-quality professional-development program failed to translate into any dramatic improvements in student learning. A two-year study of efforts to improve teachers' instructional skills in early reading reached a similar conclusion in 2008. The results are already providing some intellectual ammunition for finding better ways to select and retain effective teachers--and shedding those who are ineffective--as the best way to improve instructional quality in schools. But other scholars said it is too soon to issue a verdict on the effectiveness of professional development.