The standard of sex education in primary schools varied widely because of an inconsistent level of support for teachers.
This was a preliminary finding by Aberdeen University researchers who looked at a small sample of schools in five parts of Scotland.
In some instances, schools - and sometimes teachers - worked autonomously on sex education, with little opportunity for planning. Some teachers were uncomfortable with delivering sex education, and in one area the researchers found that responsibility was handed over to the school nurse.
In contrast, a dedicated health team in an urban authority devised support materials that were in use across the city. There was also regular training.
The researchers believe teachers need support and training to understand issues of diversity, to develop "meaningful ways" to interact with parents and other workers, and to come up with "strategies for transition".