At my son's school you find it all. And, it depends on what's going on. The teacher all have professional clothes. They don't always wear them. The bldg isn't air conditioned so the first weeks of school and last weeks of school are pretty casual. Capris are the norm with jumpers being 2nd most common and in the winter almost everyone is in slacks unless it's some kind of event day. I've gone into DS's room and found his teacher dressed up. My question to them is usually,lol,"you interviewing for a job?" I think there should be a dress code to keep inappropriate things like sports bras, tight shorts and profane language from being worn. I also think that flip-flops are not for school but for home and the beach if one is an adult.
You might want to ask your special education teacher, what the requirements are for paras. We do get rules bent for us a bit, due to the nature of the job.
.
.

. This is our first year in the public school system, coming from private schools with dress codes for the students and the staff.