By Vanessa Heaney
BBC News, Washington
US students attending sexual abstinence classes are no more likely to abstain from sex than those who do not, according to a new study.
The US government warned not to draw sweeping conclusions
Participants in special programmes were just as likely to have sex a few years later as those who did not attend.
In the past few years of Republican Party control of Congress, the spending on no-sex-before-marriage education has risen from $10m to $176m a year.
Critics have repeatedly said the programmes are not working.
They say the money would be better off spent on a comprehensive sex education that would include abstinence.
Social conservatives have long believed that teaching adolescents about sexuality and contraception could encourage them to have sex.
They would rather promote abstinence until marriage.
The students in this study, which was ordered by Congress, came from a range of big cities across the United States, such as Milwaukee and Miami and from rural communities in Virginia and Mississippi.
They were 11 and 12 years old when they entered the abstinence programmes, which lasted one to two years.
The researchers also looked at the behaviour of their peers from the same communities who did not attend the classes.
The findings show that those who attended first had sex at about the same age as their peers - at 14 years and nine months.
The Bush administration has warned against drawing sweeping conclusions from the study.