The quality of sex education is "a lottery" with some pupils not taught vital information about boundaries, according to experts.
Sex Education Forum co-ordinator, Lucy Emmerson, said teaching was too "theoretical" and failed to deliver "real-life practicalities".
This survey confirms that the quality of sex education children receive is a lottery.
Young people are telling us very clearly that teaching is often too theoretical and fails to deal with the real-life practicalities of getting help and advice or building the skills for pleasurable, equal and safe relationships.
Learning about consent is integral to good quality sex and relationships education and every school should have a planned programme which includes content on bodily boundaries, gender and power, caring for one another, feelings and emotions and how to get help and advice.
Prime Minister David Cameron has said sex education in schools must be adapted to address online pornography and called on all parents to learn how to protect their children at home.
Mr Cameron said he agreed with his Education Secretary, Michael Gove, that "wholesale reform" of the curriculum was not required, but said: "We need to make sure we are up to date on the problems of the internet. ... We should be alert to those points and make those changes."
He said the issues concerned parents and school teachers alike, adding: "We are all going to have to get better at understanding all these issues around parental controls."