Researchers have been challenged to go beyond socioeconomic status in the search for school-level characteristics that make a difference in student achievement. The purpose of the present study was to identify a new construct, academic optimism, and then use it to explain student achievement while controlling for socioeconomic status, previous achievement, and urbanicity. The study focused on a diverse sample of 96 high schools, A random sample of teachers from each school provided data on the school's academic optimism, and student achievement scores and demographic characteristics were obtained from the state department of education. A confirmatory factor analysis and hypothesis tests were conducted simultaneously via structural equation modeling. As predicted, academic optimism made a significant contribution to student achievement after controlling for demographic variables and previous achievement. The findings support the critical nature of academic optimism. (Contains 2 footnotes, 1 table, and 4 figures.)