Nearly 2,000 copies of its resource pack have been sold, mainly to schools. Manager Julie Tierney said teachers who previously felt isolated and unsupported had grown in confidence.
TSS uses a range of exercises and strategies and focuses on information and decision-making in the areas of communicating about sex, avoiding penetrative sex, contraception, sexually-transmitted diseases, getting and giving help, and relating to parents.
"The aim is to avoid taking a moral stance but to produce material based on a framework of self-respect and respecting other people which is presented in an interesting manner," said Ms Tierney. "In many areas it is relatively explicit." And that is where danger can lie.
For like the "Mars Bar" story which made headlines last year, when it was revealed a nurse at a Yorkshire school had discussed oral sex with 10-year-olds, TSS has had its own brushes with the media.
A parent complained about reference to swallowing semen as part of a quiz about pregnancy myths. Crisis was averted because the teacher and the school in Sefton received the backing of the North West Regional Health Authority, which funds the project.
"Such incidents do worry teachers though because they have to cope with the perceptions of parents and governors," said Ms Tierney.
Forty schools were initially involved in the project. By last term that had grown by another 100.
In a pilot it was found that schools that had done little sex education work took only the most basic exercises while those that already had a well-established policy used the more explicit material.
The feedback so far has been positive. Teachers gained in confidence, said sex education work improved relationships with students generally and were surprised at how mature young people were when dealing with the issue.
One unnamed teacher, who had taken contraceptives into class for use as a teaching aid, said: "I have never done sex education before and I was absolutely dreading it because I thought the students would go silly and wild and they would all start blowing them (condoms) up, but they didn't."
Many teachers who attended the first course have now started involving other staff and running parent workshops.
But there have been some problems. Some teachers have had to give presentations to governors while others, particularly in Roman Catholic schools, have used only part of the pack.
The project runs both residential and two-day courses as well as offering a helpline and pack.
Ms Tierney believed Government was sending out mixed messages on sex education. The Department of Health wants to reduce teenage pregnancies and abortions while the Department for Education, especially under John Patten, held back sex education.
However, two reports this month have proved a fillip to the work being done on the TSS project. The reports by the London School of Hygiene and Tropical Medicine and the University of Exeter confirmed that school sex education does not encourage teenagers to experiment and that it is linked to the responsible use of contraceptives.