By PHILIP ELLIOTTWASHINGTON (AP) â¿¿ The nation's high school graduation rate is the highest since 1976, but more than a fifth of students are still failing to get their diploma in four years, the Education Department said in a study released Tuesday. Officials said the steady rise of students completing their education is a reflection of the struggling economy and a greater competition for new jobs. "If you drop out of high school, how many good jobs are there out there for you? None. That wasn't true 10 or 15 years ago," Education Secretary Arne Duncan said in an interview with The Associated Press. The national dropout rate was about 3 percent overall, down from the year before. Many students who don't receive their diplomas in four years stay in school, taking five years or more to finish their coursework. Some 3.1 million students nationwide earned their high school diplomas in the spring of 2010, with 78 percent of students finishing on time. That's the best since a 75 percent on-time graduation rate during the 1975-76 academic year. The only better rate was 79 percent in 1969-70, a figure the department wouldn't vouch for. There were tremendous differences among the states in 2010. Fifty-eight percent of students in Nevada and 60 percent in Washington, D.C., completed their high school education in four years. By comparison, 91 percent of students in Wisconsin and Vermont did, according to the report. Graduation rates increased by more than a percentage point in 38 states between 2009 and 2010, the study found. Only the District of Columbia saw its graduation rates decline between by greater than a percentage point during those years. Among the most significant factors of the increase was the dire U.S. economy after the 2008 Wall Street meltdown. During the 2009-10 academic year, unemployment ranged from 9.4 percent to 10 percent.