Teaching Religion?

Hello, my question is about the extent to which a public school teacher can express or support their religious views.

U.S.A. State of Kansas. Is it legal for a Public Highschool teacher to host a youth/teenage audience Christian Bible study outside of school hours, off campus. Additionally, can the teacher ask/advertise this Bible study during school hours while he is working to any degree? Could teacher host an official school club with the same goal? Finally, could the teacher answer questions from students about their religious beliefs? Sorry for the multiple questions, I'm struggling to figure out exactly what extent of religious/worldview expression is legal for teachers. Thanks for any advice.