A new survey of teens finds 23 percent admit they have driven under the influence of alcohol, prescription drugs or marijuana. Almost 20 percent of teens who drink and drive say alcohol improves their driving, while 34 percent say the same about marijuana.

Teens are more likely to drink when they are less heavily supervised, according to the survey by Students Against Destructive Decisions (SADD) and insurance company Liberty Mutual. The survey included 1,708 high school students in grades 11 and 12, USA Today reports.

“The end of the school year and the summer months are exciting times for teens, but they are also the most dangerous,” Dave Melton, Managing Director of Global Safety for Liberty Mutual, said in a news release. “A celebratory toast can quickly lead to serious consequences down the line. These new data illustrate that there is clearly a strong need to increase the level of education around safe driving. More importantly, it’s a flag for parents to make sure they talk to their kids regularly about the importance of safe driving behavior.”

He added, “The fact that an overwhelming number of teens admit to extremely unsafe driving habits and completely dismiss any risk concern yet still consider themselves safe drivers means either teens have a different definition of ‘safe’ or we need to do a better job of educating kids about the dangers of this type of behavior.”

The survey found 11 percent of teens admitted to driving under the influence of alcohol or drugs during the summer in general; 8 percent on July 4th; 6 percent on prom night; and 5 percent to celebrate graduation.

Earlier this year, the Governors Highway Safety Association released a report stating the number of 16- and 17-year-old driver deaths in passenger vehicles increased from 202 to 240 in the first six months of 2012—a 19 percent jump from same period the previous year.