This depends on what you mean by “practiced.” Students should surely be able to practice their religions in ways that are not disruptive. However, the tenets of liberal democracy hold that the public schools, at least, should not have official religious activities.
Students should absolutely be able to do things like praying at school. They should not be able to block the hallways or disrupt class to do so, but they should be able to practice their religion. In addition, if it is a privately-funded school, the school should be able to have official religious observances.
However, in government-funded schools, there should be no official religious observances. This is because it should be up to individual students as to what sorts of expressions of religious faith they want to make. The government should not be able to require anyone to participate in any kind of religious observations.
I believe that schools should teach students the religion and what people believe in it but leave it up to the student to choose if they want to follow that religion. Religion is after all in my opinion something that gives you comfort from the unexplainable things in life. The reason its important for students to learn about religion is so that they dont accidentally offend someone of a different religion then themselves.