Copied from report linked above: " After the age-21 MLDA was implemented, alcohol-involved highway crashes declined immediately (i.e., starting the next month) among the 18- to 20-year-old population. Careful research has shown declines are not due to enforcement of and tougher penalties for driving while intoxicated, but are directly a result of the legal drinking age. Studies have also shown that education alone is not effective at reducing youth drinking (Clayton et al., 1996; Ellickson et al., 1993). To achieve long-term reductions in youth drinking problems, we have to change the environment by making alcohol less accessible to teens."
I don’t think it is strictly a crapshoot. Certainly there are cultural, regional, and social group factors at play. Is having access to alcohol important enough to risk monetary and legal consequences? Safer, cheaper, and less complicated just to obey the law, imo.