I had a very similar situation nine years ago when I first took a position in a school setting. My experience was that the teacher was looking for someone to give her a break/prep time. Although, she did not admit to that. I insisted that I would only see the students with identified needs but I was willing to do whole class instruction in a co-teaching model where she was responsible for the planning and instruction for the non-SLP kids. I was met with the same reaction you experienced. In the end, I ended up taking my kids out in a seperate group. I don't think anyone can argue with your legal responsibilities toward those children being services on ed plan. Be strong! As long as you are doing what is in the best interest of the kids you should feel good about yourself and what you are trying to accomplish. I feel your pain.