Identifying effective and ineffective schools is a central issue in education today in light of the increasing concern for student achievement and accountability. Administrators involved in school improvement projects face the dilemma of choosing from a variety of methods for measuring school effectiveness. The relationship between school effectiveness and student achievement among middle school pupils in high-poverty, high-minority-populated areas is not known. The purpose of this cor-relational study was to research the relationship between school effectiveness and student achievement among middle school pupils in a high-poverty, high- minority-populated area in Palm Beach County, Florida. The results indicated that in 2010 lower-performing minority schools (with a five-year school grade lower than an A) had lower Writing test scores than the high-performing mixed-ethnicity schools (with a five-year A grade), and also had lower FCAT Math, Reading and Science scores than high-performing minority schools and high-performing mixed-ethnicity schools (both with a 5-year A grade). Surprisingly, high-performing mixed-ethnicity schools also had higher FCAT scores in Math, Reading and Science than high-performing minority schools did, as well as higher scores for learning gains in reading, and total points earned across domains. The findings also showed that teachers' perceived school effectiveness ratings correlated significantly with student achievement. In particular, the opportunity to learn and time on task, frequently monitoring student progress, and positive home-school relations had significant positive relationships with making learning gains in reading and math. Regression analysis showed that among all teacher ratings of effective schools, time on task was the strongest and most consistent positive predictor of achievement, after controlling for percentages of poor students in schools, which correlated negatively with achievement.