Have you got written feedback from your other observed lessons? Can you identify any common areas for improvement which may indicate why the mentor has felt the need to take over? It's a tricky situation. As a mentor, I stepped in before Easter to team teach with the student teacher we had in our department because he was really, really struggling. Student weren't making an awful lot of progress and when they did, he was still re-teaching the same thing over and over because he wasn't assessing correctly to understand that they'd "got it" and needed to move on. That said, it doesn't entirely sound as though this is the case for you, since you say you've had good feedback from others. Has your mentor observed you? What was their feedback? How to move forwards....it's tricky. Check with your mentor first how they think you are progressing. Just explain that you are a little concerned because you feel as though this means you aren't progressing. Highlight previous feedback and just say that you really do feel you've got the ability to get back on track by yourself, taking on board all advice. I do think the team teaching is a little bit heavvy handed. If the teacher is unwilling to leave her class in the hands of a student teacher, the group erally shouldn't have been put on your timetable. Some teachers really do get worried about their classes' progress when taken over by a trainee, but it doesn't sound like you're doing too much damage if you've only had one bad lesson. You do need to speak up - albeit diplomatically - unfortunately. I know it's awful, but it needs to be done and it's part of being a professional. Your mentor IS the person to speak to. I've had to over-rule my HOD before when she insisted that the trainee had certain classes on their timetables. It's your mentor's job. If the HOD wanted final say, she should have mentored the trainee herself.