My S went as a junior in 2013 - we took him on our own. His school did not go. It was a fantastic experience in many regards. He did get some prescreen/audition waivers and a few scholarship offers out of the experience. I’m not sure if all the schools are doing things the same way this year. He learned quite a bit from the audition - by doing his own and getting feedback from auditors, but also from watching the others in his group of 30.
Here are a few related SETC threads that might interest you. I - and others - have also posted our experiences on other threads.
http://talk.collegeconfidential.com/musical-theater-major/1749523-thoughts-from-setc-2015-p1.html
http://talk.collegeconfidential.com/discussion/comment/18204562#Comment_18204562