Hmm, as a Christian student studying to become a health care professional, I have to take off my cross because it would be impractical for both H&S reasons, and also because some people have specific reactions/wouldn't say certain things (relevant to treatment) if they knew I was Christian. I don't see the difference - children need to be able to see lip movements/facial expression to understand how to form a language, so surely the teaching assistant's issue is not one of religion, but one of being able to do the job you're paid for efficiently and safely (the same as mine).