The purpose of the study was to assess science achievement of 11th grade students. Science achievement was assessed in knowledge and inquiry domains. The knowledge domain included three sub-areas including memory, understanding and application. The inquiry domain was divided into four sub-areas involving identifying problems, designing inquiry, data analysis and drawing conclusions. The results indicated that overall science achievement of the 11th grade students who participated in the study was at the proficient level. Regarding the knowledge domain, the achievement in the understanding and application areas was at the proficient level, and the achievement in the memory area was at the basic level. In the inquiry domain, the achievement in all the sub-areas except the identifying problems area which was at the basic level was at the proficient level. There were no gender differences in overall science achievement. However, gender differences were found in all the sub-areas except the application area and varied across the sub-areas. Also, there were significant differences in science achievement among regions.