by Daniel R. Levine

About the author: Daniel R. Levine is the Washington bureau senior editor of Reader’s Digest.

Author’s note: Names of the teen-agers in this viewpoint have been changed to protect their privacy.

Eighteen-year-old Mike Woods of suburban Cleveland describes his schedule this way: Every day after school he smokes marijuana. Then he takes a nap or calls a few friends and just “hangs out.” Before he started smoking pot three years ago, his grade point average was 3.5, and he was a star sprinter on the track team. Now his GPA is 2.7, and he has dropped track.

“Pot makes you lazy,” says Woods. “I don’t like to do schoolwork.” Even so, he admits he’ll continue smoking marijuana. It...