This volume in the Harvard Education Letter Spotlight Series provides a tool kit for principals and administrators seeking to improve the quality of classroom teaching in an era of increasing accountability. The No Child Left Behind Act of 2002 mandates that all teachers be ""highly qualified"" by 2006, although the criteria for meeting this standard are vague at best. Meanwhile, half of the nation's teachers are expected to retire by the end of the decade, and turnover among new teachers is high: 30 percent leave their jobs within three years and 50 percent leave within five.