"Many teachers are anxious about teaching body parts, facing intimate personal questions and not having sufficient knowledge to answer queries that may come up in class," says Neal Pettit, PSHE teacher at the Howard School in Rainham, Kent.
"But teenagers often get their information from television or from parents and have a distorted view of the facts, which can put them at risk. To tackle these tricky issues a teacher needs to be confident in the subject."
The National Aids Trust (NAT) has produced a free practical resource pack for teachers which it hopes will address the problem. It's full of ideas on how to integrate HIV into the national curriculum for key stages 3 and 4 (P7-S4) - not only in PSHE classes, but in citizenship, science, geography, ICT, drama and English.
Nick Wergen, head of English at Sackville School, says: "The message about HIV and Aids needs to be reinforced again and again to really get through, so tackling the subject across the curriculum is a great idea.
"The NAT pack will relieve the anxieties of many teachers. The materials are teacher friendly, with easy to use, tightly structured lessons that support them and their students through the topics in a focused way. There are lots of activities that will help to separate the myths from reality.
"The issues are handled subtly and sensitively and the language used is carefully chosen so as not to perpetuate stigma and discrimination. This is especially important if you have a pupil in your class whose life is affected by HIV."
According to NAT, there are around 1,200 HIV-positive children living today in the UK, and an additional 20,000 children living in a family where one or more members is HIV-positive.
The pack was developed with the support of the National Children's Bureau and is available free to all secondary schools in the UK. It includes lesson plans, factsheets, posters and ideas for assemblies and fundraising activities.
Among the ideas in the pack are: science lessons looking at how the growth and reproduction of bacteria and replication of viruses can affect health, and how HIV is transmitted from one person to another; a citizenship, geography and ICT project exploring the impact of HIV on a chosen country socially, economically and culturally; art and design projects looking at Aids awareness campaigns; and English and drama projects looking at living with HIV
Teachers can order a pack online at: www.worldaidsday.orgschools1.asp