Good post by perryplatypus. I agree with the reason behind the pushing possibly being about personal space. In my school, we have children who find lining up very difficult. One strategy is to stop expecting those children to line up. They join the line at the end as it moves off, when they feel comfortable. Another reason for pushing can be the lack of awareness of social rules about joining in. Pushing may be your ds's way of joining in. He might need a "social story", which is essentially a picure, or series of pictures to help him understand what works and what doesn't. Social rules and communication are very complex, and lots of children need additional help, and sometimes, direct teaching about what those rules are and how to negotiate them.
Visual timetables can also be very helpful. I would suggest that to start with, he has an individual one (even if there is a class one as well). Ideally, he should be able to choose some of the symbols to put on so that he makes some choices, but that also, some of the things are fixed and non-negotiable - e.g. playtimes, phonics etc.
I think you need to become a pushy parent! The teacher has 30 children to look after and although she will be doing her best, it may take the extra push from you to get things moving. (I say this as a committed teacher - it's not a criticism of the teacher, just the way that things can be at the beginning of the year).
Here's what I would do:
Speak to the SENCO & class teacher together
Ask for a referral to the autism team/beahaviour support team etc.
If external agencies are involved (which I presume they must be if he is being assessed), then he should be on School Action Plus stage of the Special Needs list. Agree 3 targets that everyone will be working on with your ds. These should include details of what strategies will be used, over what timescale, who will be using the strategies (teacher, TA, lunchtime supervisers etc.)
Perhaps it would also help if you started a new message with the word autism or ASD in the title, so that people on here with similar experiences can help you.