Don, one thing to remember is that a lot of state schools in Europe (including the UK) have uniforms, and therefore a uniforms policy. When these cases arise, they usually result from a violation of the uniform policy - extending a privelege to those of a religious persuasion which isn't enjoyed by the rest of the school body. If certain forms of self-expression are denied to the rest of the kids, one could argue, why are some forms allowed to others?

Whether you think freedom of religious expression is sufficiently important to warrant the relaxation of the school rules for some pupils is probably a separate issue, but I personally support the basic principle of school uniforms.