All schools should make parents and pupils aware of the right to opt out of acts of collective worship or religious observance, a report has said.
Academics at the University of Leicester said there is no reason why children should be expected to participate and said the current practice means that those that do opt out are at risk of discrimination.
The majority of schools in the UK are required by law to organise acts of collective worship (England, Northern Ireland, Wales) or religious observance (Scotland) for their pupils.
The report recommends that governments in the UK should urgently consider afresh the rationale underlying these duties.
The authors argue there is currently no accepted rationale, and only when one is agreed can an informed debate begin on whether the current duties should be maintained or amended. They said that if no rationale can be found for a collective activity in schools, then the current duties should be abolished.
The report said: "Where the aims for the duty of collective worship are set out (e.g. in the English and Welsh Circulars), these appear contradictory in the context of a diverse pupil population, specifically the aims to provide an opportunity to worship God yet simultaneously to develop a community spirit and promote a common ethos.
"Furthermore, there is an inherent tension and contradiction between the presentation of collective worship as inclusive and appropriate for all, and the existence of procedures for disapplication and withdrawal on the grounds that it might not be.
"In Scotland the arguably contradictory nature of the policy guidance poses the question of whether it is possible to practise religious observance in a way that can include all pupils when beliefs are not shared within the school community."
The paper recommends that all educational authorities in the UK issue guidelines to schools to clarify that the right to withdraw from acts of collective worship/religious observance extends to all schools.
All schools should also clearly publicise the content and format of acts of collective worship/religious observance, so that parents and pupils are knowledgeable about what happens during these activities, and able to make informed decisions about whether to opt out.
It also suggests all schools should provide appropriate alternative activities, with educational value, where opt outs have been requested.
Keith Porteous Wood, executive director of the National Secular Society, said: "The requirement for schools to hold worship is hopelessly outdated and completely inappropriate where most young people are not religious and those who are come from a multiplicity of faiths.
"Laws that mandate worship are an obvious affront to children's religious freedom, usurp parental rights and go well beyond the legitimate function of the state.
"The right to withdraw from school worship is neither a practical nor an acceptable compromise. It inconveniences schools and leaves pupils ostracised, so parents wishing to withdraw their children are left in an impossible position."
A Department for Education spokeswoman said: "Collective worship plays an important role in schools. It encourages children to reflect on belief, and the role it plays shaping fundamental British values of tolerance, respect and understanding for others.
"It is for schools to tailor their provision to suit the needs of their pupils, and parents can withdraw their children from all or any part of collective worship."