A new study by Mathematica Policy Research, Inc., suggests that abstinence education has no real positive or negative impact on the sexual behavior of young people. Participants were no more likely to abstain from sex than the control group. Conversely, they were also no more likely to have unprotected sex.
While I don't find the results of the study that surprising--telling 12 year olds not to have sex doesn't really seem that useful--I was surprised to learn that Mathematica has a policy research arm. After some research, I was disappointed when I learned that Mathematica, Inc. isn't the company that makes Mathematica (that's Wolfram, Inc.) but an older company that does policy research. I thought they were going to suggest that abstinence education should be replaced with more math and science education, which studies have shown promotes abstinence through high school.
The full study is available here if you're interested.