The public education system in the United States has received a great deal of attention from both constituents and policy makers alike over the past thirty years. Identifying less efficient school districts and examining the sources of inefficiency has important policy implications. School districts might improve efficiency by managing educational resources differently. In this paper, we estimate technical efficiency for all three types of school districts in the state of Illinois K-12 public education system. Technical efficiency in the Illinois school system averaged 90% for unit school districts, 85% for elementary school districts, and 82% for high school districts. We also investigate possible factors associated with inefficiency. The percentage of student enrollment that qualifies as low income and the size of the school district are positively related to inefficiency. School districts that have a larger percentage of teachers with advanced degrees are more efficient. Having a lower ratio of students per administrator in a school district increases technical efficiency.