I had a similar situation this year. A student wanted the other chemistry teacher and told me this the first day of school. I blew it off as a child wanting her way. I will never do this again--this student made last year miserable for me. She was constantly going to the Vice-Principal and "reporting" me. She could not learn in my class, I did not teach, I spent sll my time on the computer. I got called in 6-7 times because of this student. I now say go let someone know and just get them with the teacher that they want if they really want it badly.