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States with the worst schools

10. Oklahoma • State score: 64.2 • High school graduation rate: 73.9% (20th worst) • Per pupil expenditure: $9,075 (8th lowest) • Preschool enrollment: 43.5% (19th lowest) -- Oklahoma received low marks from Education Week in a number of major indicators. The state received a D in student achievement, driven in part by poor proficiency scores in reading and math, especially among eighth graders. Students also lacked the opportunity to succeed. Young adult Oklahomans were among the least likely Americans to pursue a higher degree, and state adults were among the least likely to have a postsecondary degree. The state also received a poor grade in school financing, due in part to limited per pupil spending. Yet, Oklahoma got an A in standards, assessments and accountability, ranking among the best states in the nation. | Photo by Thinkstock

Gallery: States with the worst schools

By Thomas C. Frohlich and Michael B. Sauter, 24/7 Wall St.

For years, American students have consistently ranked poorly compared to most developed nations. And according to a recently released study, the U.S. education system remains mediocre, receiving a C− grade, for the third year in a row.

The K-12 Achievement Index, one indicator in Education Week’s recently released “Quality Counts” report, measures key education outcomes and provides ranks and grades for each state based on their commitment to improve educational policies and practices. 24/7 Wall St. reviewed the states with the best and worst scores for K-12 achievement.

Yahoo Homes is publishing the states with the bottom 10 scores in K-12 achievement here. Click on the slideshow above to see them. To see the full report, including the states with the highest scores and the study methodology, go to 247WallSt.com: