How sad. I would think any religious leader would be happy to see a 12-year old boy wanting to go to Church, not matter what they are wearing.

I have only ever gotten compliments while wearing a kilt to my church (Unitarian Universalist) and have gotten compaints when I show up in pants.

I can only hope that the bishop would be willing to explain his stance so that he doesn't drive your son away from attending church.