'he's not learning' Wow.
I bet they back track by the time you get to the meeting.
Do you want more help for ds? - (is 'ongoing SALT and OT' an ongoing battle for it, or do you already have it?). Are you wanting an assessment of SEN for a statement, or a reassessment of an existing statement?
If any of those things, then Please, please consider going softly softly, ever-so-nicey to the meeting and see if you can manage to get them to repeat any area where he is not learning, and get some written record.
This ever-so-nice stuff is because staff tend to become very defensive if they feel under attack. If they feel you are blaming them they may do their level best to think of some instance of progress to defend their record.
The TA may have been thinking that his numbers and letters weren't progressing, or maybe it is the SEN side, and her efforts to teach social skills, or manage sensory issues does not seem to her to be working.
But either way, if you can get them to repeat any area or areas where he is not learning it is your passport to getting more help. Especially if you get a written record. Generate one yourself by an ever-so-nice email if you have to.
Absence of progress either in mainstream subjects or SEN areas is a Code of Practice marker for taking another good look.
And yes, track through each SEN and see what they are doing as a work-around (changing the environment), and what they are doing to make him less prone to having the difficulty. eg for social skills, having support in the playground and a buddy programme is the work-around - changing his environment, and SALT is teaching him social skills to make him more able to function in a mainstream environment.
And if he isn't learning, it will be what more they need to do to help on each of those headings
Of course I am fuming with you, big time, but hoping it will turn out to be a good outcome for you and ds