Many primary school teachers feel "uncomfortable" about tackling issues such as homosexuality and contraception in the classroom, a study has revealed.
The report said better training may cut the variation in what is taught
Abertay University found that some had "tinkered" with the sex education programme to lessen embarrassment.
The report, based on responses from 118 primary schools in Tayside, said it was vital that every teacher who delivered sex education had adequate training.
NHS Tayside recently began relationship and sexuality training for teachers.
The Scottish Executive-commissioned study revealed that teachers overwhelmingly believed the provision of sex and relationship training was an important aspect of their role.
The vast majority of parents were comfortable with teachers talking to their children about sex and relationships, according to the report.
However, researchers found some teachers admitted to "tinkering" with the programme.
"The Scottish Executive and local authorities are increasingly demanding that primary school teachers become sexual health promoters," the report stated.
"However, as both this study and others have found, many teachers are uncomfortable with aspects of this role.
"Even when teachers claim to be comfortable teaching sex and relationship education, this is often only after tinkering with the programme."
"Other subjects also caused some concern, particularly homosexuality and contraception, although a number of teachers also cited potential questions about oral sex," it added.
The research revealed that, despite the fact that the three councils covered by NHS Tayside recently rolled out a sex and relationships programme, there was still a wide variation in what was taught.
It also found awareness of sexually transmitted infections was the least covered topic in the curriculum, with 57% of primary schools not teaching about STIs.
With Scotland's high rates of STIs and teenage pregnancy, compared with other Western European countries, the report said it was sensible to ensure all teachers had the requisite training to help them.
Such training might help cut the variation in what is taught, it argued.