If you are shadowing, then as Summer has said, it will be at your normal rate. Usually you'll be released from your normal duties for a while.
Although, again as summer has mentioned, you should be paid a higher rate for taking music lessons more often than not you won't be. I don't but I've never pushed it mainly because I teach musical instruments and we've very few staff who can do this. If I said I wouldn't do it for the money the children would miss out. Plus I enjoy doing it.
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Accept that some days you are the pigeon and some days the statue
