Christians have defended their work in schools following strong criticism and accusations of proselytisation from the National Secular Society.
The NSS claims in its new report, 'Evangelism in state schools', that publicly funded schools are being "targeted and exploited" by evangelical Christian groups with the aim of converting young people to the faith.
"We do not doubt that pupils' education can be enhanced by the input made by external contributors, but it appears clear from the evidence that many external school visitors are primarily concerned with evangelisation rather than education," the report states.
The NSS says parents and schools should be "deeply concerned" by evangelical Christian groups providing religious education, school worship, pastoral work, prayer spaces and Bible-based clubs in state schools "without parents' knowledge and with little, if any, opportunity for withdrawal".
It claims that such activities represent a "significant and growing incursion" of evangelical organisations into publicly funded education, and compromise the objectivity and integrity of state education, as well as the human rights of parents who do not share their religious values.
"[A]s a matter of principle we believe there should be no place in publicly funded schools for evangelism and proselytisation," the report says.
"We therefore regard it as disturbing that in schools right across the country religious organisations are being given a platform to evangelise."
Key recommendations outlined in the NSS report include the issuing of national guidance to schools setting out best practice for working with external visitors and contributors, particularly where these are religious groups.
The NSS also calls for all schools to publish and adhere to an external visitor's policy which forbids proselytising and evangelism and makes clear that parents should be informed ahead of visits.
Youth For Christ, one of the organisations named in the report, said in a response that it would welcome the development of best practice guidelines.
"As a well-established youth work charity, working in Britain for over 65 years, we have always sought to serve and support schools on their invitation," it said.
"Our staff and volunteers are trained, many to a professional level, to act as responsible youth workers within an educational context serving in teaching, chaplaincy, reading and classroom support, sport, dance and drama.
"We would welcome the development of best practice guidelines for external visitors and believe they would enhance our professional approach."
Also mentioned in the report is Christian charity Counties UK, which has been operating its GSUS Live resource in schools for the last 13 years.
The technology-based programme is geared to the Religious Education curriculum at Key Stage 3 and explores the topics of fear, forgiveness and rejection.
Counties said the programme had proved very popular with secondary schools "because of its educational value" and that all GSUS Live presenters received mandatory training "which emphasises that the purpose of the programme is education, and not evangelism or proselytising".
It added that the programme's content was "fixed" and made known to schools in advance, and that Counties required a member of the teaching staff of the school to be present throughout the visit.
"Counties works in line with national guidelines to help schools present what Christians believe about Jesus - not what children should believe," the charity said in a statement.
"We encourage children to foster a spirit of enquiry and for them to question, challenge and form their own opinions. Counties does not proselytise in schools."
Dr Dave Landrum, director of advocacy for the Evangelical Alliance, defended the contribution of Christian groups to schools.
"Schools work with Christian groups because they are valued, because they are trusted, and because they contribute to the overall wellbeing of students," he said.
"There is no such thing as neutrality and across the world religious belief is growing and our schools need to be plural rather than secular spaces where faith groups can openly and fully take part.
"The curriculum requires a spiritual dimension to education and Ofsted have found that religious education needs improvement. In a choice of education or no education the National Secular Society would seem to prefer pupils were ignorant about religious beliefs.
"This is no more than the latest desperate and ultimately doomed attempt by dogmatic secularists to remove faith from public life."