I totally understand your frustration CK_10. I find it very frustrating when parents and teachers want to put everything on us. Trying to prevent problems down the road, I have started showing parents and teachers a little diagram at the begining of me seeing the child. It is a simple triangle with me at one tip, the parent and teacher at another tip and the child at the third tip. My role is specialist, to show the child how to make the sounds, help build the structures for language development etc, the parent and teacher's responsibilities are to carry over the things the child learns in therapy. I have given parents the model of physical therapy. If you go to your physical therapist and he gives your child daily exercises to do during the week, do you think the PT is going to follow you around and make sure your child did them? No and neither am I, it isn't the best use of my time with the child. Once we are beyond me teaching them the basics, it is our team's responsibility to make sure we are practicing the newly learned skills.
CK I know that might not fix this current situation but it one way I have tried to head off that the IEP team for speech suddenly equals just me. For your current situation I would use that approach, reminder them we are a team. I would also remind them that communication is not isolated to just your sessions, even if you happened to see this child every single day, communication would still be happening outside of that time and therefore needs to be monitored by other IEP team members. Another possibility you could try if the teacher and parent are resistant to carry over is to schedule consultative time each month or week with them to make it easier for them.
I feel you dilemma and know it isn't easy to deal with. I have a couple of kids on my caseload who did not qualify by test scores or my opinion but I was forced to keep them mainly because the School Psych decided that nope, the kids issues were language, even though I, the language expert disagreed. I will get out of schools eventually because of crud like this. One of the kids that I was forced to keep - now suddenly is doing so well they are talking about exiting her from special ed. Feel like telling - told you so! But of course I will only think it. :-)