This study evaluated the effect of online instruction on the academic achievement of K--12 students in ten states as measured by the percentage of proficient students in reading and mathematics at the school level. We used publicly available data provided by the Department of Education in Florida, Michigan, Minnesota, Nevada, Ohio, Pennsylvania, South Carolina, Utah, Washington, and Wisconsin. Although the online schools do not appear to perform better than the traditional schools, on the average, their performance is not homogeneous. Some schools appear to perform as well as or better than traditional schools.