Science achievement gap between fifth, sixth, and eighth grades and boys and girls in low and high performing schools were under investigation in the present study. In accordance with this purpose, three schools were selected to represent high performing schools and two schools were selected to represent low achieving schools for their performance on a nationwide exam. A total of 612 fifth, 816 sixth, and 604 eighth grade students in high achieving schools and 231 fifth, 364 sixth, and 328 eighth grade students in low achieving schools constituted the study sample. Students' end of semester science grades were used as their science achievement measure. Results showed that students' science achievement decreased from 5th grade to upper grades both in low and high achieving schools. In addition, they showed girls' science achievement was higher than boys in several grade levels both in low and high achieving schools. Finally, results showed that science achievement gap between genders is more evident in high achieving schools.