I am a middle leader at a SEND school (slightly different than mainstream I know) and we have done the TA appraisals for the past few years. We have changed the way we did it this year as the previous way was ineffective and simply a tick box exercise.
A lot of the TAs preferred it with middle leaders as they felt more comfortable and that we had a better understanding of rhe day to day roles they had due to us a being in classes still. However, I found it was important to set out with SLT what we could and couldn’t offer for TAs before hand ie; can we ok them to go on certain courses, were we OK to allow them time to shadow other staff etc. It was also really useful to set out at the start of each cycle that it wasn’t an opportunity to complain about things at work but that it was a celebration of their skills and development over the year and goal setting/training discussions.
I uses the TA appraisal system.overhaul as part of my NPQSL training and one thing that did come up was that we needed to have a stronger monitoring system so we could check on their development throughout the year and whether they needed further support as this was something SLT didn’t have the time to do.
I hope this is helpful, good luck