Abstinence-only sex education programs are not effective in preventing or delaying teenagers from having sexual intercourse, according to a report released on Friday by Mathematica Policy Research, the Washington Post reports (Sessions Stepp, Washington Post, 4/14). The report, which was commissioned by Congress, followed 2,057 U.S. teenagers in late elementary and middle school who participated in four abstinence programs, as well as students in the same grades who did not participate in such programs.