The ring is not a christian symbol so goes against the schools policy of no jewelry in class. What's wrong with that?
Who decides whats a Christian and whats not? Technically headress isn't muslim garb either. And technically nobody in a public school should have a kirpan (knife) either. To carry the Kirpan you must be a saint first (aka, able to have complete control over all vices and be immersed constantly in the five virtues) and THEN you can carry a kirpan.
Most kids , no matter their faith, fail this.
The problem to me, seems to be that two different movements emerged to the old problem, where the majority supressed minority religions and forced their religion down the throats of everyone else.
One school of thought was to supress the majority religion as well, thus no religion gets special treatment.
The other school of thought was to allow minority religions the same rights to flaunt their religion down everyone elses throats.
The problem is both plans were set in motion, now you have a situation where Christianity really is under an unfair set of restrictions. Just pick a solution and stick with it.
Either no religious exceptions, or allow everyone to walk around with giant crucifixes and bible pages plastered to their face and stay out of it.