This study investigated the variables affecting the science achievement of eighth-grade students by multi-level regression analysis. The variables included in this research were students' attitudes, confidence level, value, engagement in science, socioeconomic status, school type, school region, and teacher experience. The study group consisted of 1049 students and 41 teachers. In the first research question, differences in students' science achievement scores among their schools were investigated. According to the results, the students' achievements differed among their schools. Approximately 16.3% of the differences observed in science achievement were stem from the differences among schools, and 83.6% stem from the differences among students. In the second research question, student characteristics that explain the differences among the science achievements of the schools have been examined. Students' socioeconomic level, attitude, and confidence level were only variables that have statistically significant relationship with achievement. Socioeconomic and confidence level variables have a positive effect on achievement, but attitude variable has a negative effect on achievement. In the third research question, student and school characteristics that affect science achievement have been examined simultaneously. The school characteristics that have been included in the regression model were teacher experience, region, and school type. It was determined that none of the regression coefficients for the school characteristics variables were statistically significant in the regression model.