The father of a buddy of mine told him about how he and his friends used to drive from their Minnesota town, where the drinking age was 21 during the 70's, to Wisconsin, where it was 18. "We'd get wasted and then drive back to Minnesota, which probably wasn't a good idea...but things were different then," he explained.
Things were different then. Cars were less safe, less people wore seat belts, there were probably more drunk drivers on the road and they were probably less likely to get pulled over for DUI.
Things have since changed for the better. Statistics show (a bit outdated) young people started taking drunk driving more seriously during the 1990's, and consequently, they are less likely to do it than their parents were at the same age. Some, such as Mothers Against Drunk Driving, attribute some of that success to a higher drinking age. As unfair as I believe the 21 drinking age to be, I think there may be some truth in that argument.
What the 21 drinking age does is encourage teens and young adults to drink secretively and probably more dangerously. They are more likely to go to house parties, less likely to go to bars. However I also sense they are less likely to drive drunk.
First, the penalties for an underage DUI are harsher. You're busted if the breathalyzer detects any amount of booze in your blood. While you also run the risk of getting slapped with a drinking ticket by simply attending a house party, the consequences of such an offense are relatively minor, whereas the shame, revocation of a driver's license and the black mark on your criminal record resulting from an OWI conviction are things that most youngsters take seriously.
More importantly, however, has been the cultural shift against drunk driving in recent decades. A strong distinction between drinking and drinking & driving has emerged. All you need to do is read the UW student press to see evidence of that thinking. The student papers, while typically opposed to restrictions on student drinking, are decidedly less tolerant of OWI than older Wisconsinites. While many in older generations, including most Assembly Democrats, were reluctant to oust embattled Rep. Jeff Wood (I-Bloomer) after his multiple OWIs last year, the student press seemed to think his resignation was a no-brainer.
The drinking age is a bad idea. But some of its effects may have been positive. The way to retain the benefits and reduce the negative effects would be to allow 18-year-olds to earn drinking licenses by taking alcohol safety courses. If they are caught driving drunk or getting into fights, their drinking privileges would be revoked.