Some students at Mirfield Free Grammar have said they no longer have access to facilities to pray inside the building.
The school, near Huddersfield, said it was "a broadly Christian Academy" and sixth form students could leave the site to attend a mosque.
A solicitor representing the pupils and families said the next step depended on the school's further response.
Yunus Lunat said: "It's a management issue. It should never have got to this stage, it's been going on for more than a year and I'm amazed that it's not been resolved.
"The problem is that they are told they cannot pray within the school building and so they've met the challenge - which is part of life - by going outside of the school on the grass verge or on the concrete and that has resulted in disciplinary warnings issued to children."
The students told BBC Look North that up until September 2014 Muslim students at the academy had access to prayer mats and space indoors where they could pray.
The pupils said the option was "withdrawn without explanation" and now they had no choice but to worship outside.
Pupils said travelling to the nearest mosque, praying and then travelling back to school would make them late for subsequent lessons.
In a statement, the school's executive principal Lorraine Barker said: "We are a broadly Christian Academy and have never had a prayer room.
"Before students join the sixth form, we make them aware of the facilities we have on site and we make it clear we do not have a prayer room.
"Sixth form students are welcome to leave the site to attend their own mosque, however, local mosques have offered their facilities to them if this is more convenient."
Mr Lunat said he believed there was a case he could take to court "otherwise I wouldn't be here, we wouldn't be doing this".
The Department for Education said it was a matter for the school to deal with.
A school may face legal action from a group of sixth form students who claim they have been forced to pray outside.