In all the districts where I've worked, the counselors are on the teacher pay scale, so not an advancement- more like a lateral move. But people seemed to think I was "moving up" when I went from teacher to school counselor. Probably because I was out of the classroom.
I'd go in with cold, hard facts. Will doing your practicum mean they won't have you in the classroom? That could be problematic. I would spell out what this internship would mean for the school- advantages to having your in the counselor internship position (now and in the future) and also stress and specify how little it would impact the school negatively. If it does mean that you'll be out of your classroom, then make sure you have a plan for how that will work in a way that impacts students and staff as little as possible.
I also posted some links in a thread below about convincing administration of the importance of counselors in schools. I will c&p that post here: