Washington, D.C. ? Teenagers say drug problems at school are getting worse, and parents express doubts about ever making such schools drug free, a new study says.

The percentage of teens who say they attend high schools with drug problems has increased from 44 percent to 61 percent since 2002, and the percentage in middle schools has increased from 19 percent to 31 percent, according to the survey to be released today by Columbia University’s National Center on Addiction and Substance Abuse.

Four in five teens in high school told researchers they have witnessed the use, sale or possession of illegal drugs on high school grounds, or seen someone who was drunk or high on campus.

Some 13 percent of teens said they had tried marijuana.