I have a child with undiagnosed SEND in my year 6 class. We are applying for an ehcp for him at the moment. He's in there with 4 others with ehcp's. I don't have a TA.
Like your son, this child is mostly ok and was fine in school in small bubbles, until he wanders/bolts off/ is asked to do something he doesn't want to do. Like your child, he will often run off across the field, climb trees or buildings, and become violent.
Whilst I do everything I can, and give him this/then boards, visual timetables, brain breaks, tailored teaching etc it is not enough. He is constantly on the verge of expulsion. I have to evacuate the class around him on a regular basis amd so far this year he has thrown rocks at me, kicked me, attempted to bite me, and come at me with scissors. Exclusion is very, very hard to put into place. Frankly, for this child, a special setting or a PRU would be better. Sometimes school is not the best setting, particularly for PDA children. Your sons teacher will also be coping with the rest of the class and it is horrible to see the effect of other childrens violence on them.
Sometimes other settings are better for all concerned and it is easier and better to get that setting in place before transferring to secondary when ultimately most settings have few if any places left.
I can cope with all manner of abilities and needs in a classroom and currently also have 2 working at reception level, but I cannot cope with violence and most primary settings can't - and neither can the other children. Engage in dialogue with the SENCO, investigate diagnosis and alternative settings. They can be flexible. A child I taught last year is now in school for 2 lessons in a nurture group and in a special setting for the rest of the day, for example.