“Teen marijuana users are approximately twice as likely as non-users to drop out of high school.234 One study found that, compared to students who did not use marijuana at all in the past year, those who used marijuana less than weekly were 2.6 times as likely to be school dropouts (5.8 percent vs. 2.2 percent) and those who used marijuana at least weekly were 5.8 times as likely to be school dropouts (12.8 percent vs. 2.2 percent).235 Students who use marijuana before age 15 are twice as likely as other students to report frequent truancy and three times as likely to leave school before age 16.236 One study found that, by their 40s, individuals who used marijuana in adolescence and young adulthood had more than a third of a year’s less educational attainment than non-users. The more frequent the marijuana use in this age group, the fewer the number of years of educational attainment achieved.”

Source

"Adolescent Substance Use: America's #1 Public Health Problem," The National Center on Addiction and Substance Abuse at Columbia University (New York, NY: National Center on Addiction and Substance Abuse at Columbia University, June 2011), p. 57.
http://www.casacolumbia.org/a…