15 and 16-year-olds in schools across Brighton and Hove have been invited to take a chlamydia test as part of a personal, social, health and economic (PSHE) lesson.
While not compulsory, students can take the test without informing parents and without their consent.
The scheme is in line with government guidelines to try and reduce the spread of sexually transmitted diseases among young people.
But some parents have complained that their children felt uncomfortable or humiliated by the tests, and argued that parents should have been told about it.
Brighton and Hove Council, which runs the scheme, said it was "entirely consistent with government guidelines".
NHS guidance from 2012 says under-16s can be offered STI tests without their parents' knowledge, but only if they can't be persuaded to tell their parents.
Blatchington Mill School (BMS) says it has only had one complaint from a parent, which it is taking seriously.
It released the following statement on the school website:
"Blatchington Mill School works in conjunction with our local NHS Provider, Sussex Community Trust and Brighton & Hove Council, to provide a PSHE programme that is directly in line with local directives.
"At BMS we recognise the challenges of growing up and making positive and healthy decisions about relationships. As an integral part of our PSHE curriculum, students are made aware of confidential sources of information and support. These confidential sources of help include helplines, websites, local young person's advice centres and local sexual health services. This aims to empower young people to access support services, including sexual health advice and treatment if they require it.
"We would like to share responsibility with parents/carers in the delivery of relationship and sex education. Parents and carers have the right to withdraw their children from all or part of the sex and relationship education provided at school except for those parts included in the statutory Science National Curriculum. Parents and carers who wish to exercise this right can contact the head of PSHE."
Sarah Pervical is from Romance Academy, a Christian organisation that delivers sex and relationships education.
She told Premier's News Hour that it is good that the subject is being brought up in schools, but adds that parents need to be involved in the conversation:
Photo: Petra