I don't remember if my school had a dress code or not for class.

However, there was definitely an unwritten dress code. How do I know this? I lived in shorts and a T-shirt (not the SAME ones every day, of course), and this was apparently too casual.
When I was on my rotations, I nearly always wore a skirt with hose and closed-toed shoes, because that was the dress code. But I noticed that my fellow students were much more casual. One even showed up to our rotation site in frayed blue jeans. Granted, it was a weekend, but that definitely would have gotten her into trouble had anyone from the school seen her. In fact, one of my preceptors (who'd gone to my school) told me he'd been sent home one day for not wearing socks with his loafers. Now THAT's conservative.