If kids are not allowed to make even simple decisions for themselves like what to put on when they get up in the morning there should be no expectations that any decisions they make will be good ones. They need to practice making decisions. Even if their decisions are not the ones we'd make they need to be able to make them.
Clothes are a great one for them to do. The consequences of these decisions is not much. Either the kids in the classroom think they are uber cool with what they wear or they make fun of them and the child learns a quick natural consequence.
If they dress in summer clothes and it's winter outside they quickly learn that putting on pants and a coat along with shoes that are enclosed might be a better choice.
I have only had a couple of times where my granddaughter made poor choices in her clothing when it mattered. I let her experience the consequences in a somewhat safe way and she has NEVER made those choices again.
When she was little she would take off her shoes and socks every time we got in the van. I would have to get in the back and have a seek and find mission to dig them out of the back, under her seat, under the passenger seat, where ever she tossed them.
I had repeatedly told her she needed to leave them on since her feet would get burned on the hot concrete if she didn't have shoes on or that her feet would get cold if she had to walk without her shoes when it was cold.
One day I had enough. I got out of the van and once again she was barefoot. It was snowy outside. I park the van about 12-15 feet from the front door, the sidewalk was shoveled. I plopped her down on the snow in the side of the driveway and walked off towards the door.
She started screaming to be carried. I said OOPS! Looks like you forgot to keep your shoes on! Better hurry up, your feet are going to get cold since you forgot to keep your shoes on. She ran to the door and to this day has never taken her shoes off in the van again.
She learned that when she doesn't keep her shoes on that her feet might get cold.
A different time I reminded her again and again to wear a heavy coat outside for activities because it was very cold. She had a BMX race one day and I reminded her to wear her heavy coat. She wore a lightweight denim jacket that actually goes over a sun dress.
It was very very cold out that day. She was shivering on the top of the gate. One of the parents had a propane heater set up inside a tent so she could get warm during the time she was not actually racing so I felt there was no "real" danger. I let her wear that jacket all that day. She was not outside of this tent where it was warm enough to go in shirt sleeves for more than 5 minutes at a time. She didn't even get a runny nose from this event.
She has never gone outside when it's cold or even cool without her coat. If she gets too hot she will take her coat off but all in all, she wears her coat.
Do I feel mean about these actions? I feel really bad about the cold day because I know she was deeply uncomfortable. BUT she learned one of the most important lessons she might ever learn. If she doesn't dress for the weather she will suffer.
So, let your kids pick out what they are going to wear. Go to their rooms with them at bedtime and let them pick out their clothes for the next day without you telling them this is what they are wearing. Let them go mismatched and goofy if that's what they want. They'll only do it once if the kids make fun of them, if they like it and feel original they'll do it every day.
What they wear to school really doesn't matter as long as it is clean, not worn out and in need of repair, and it doesn't distract the other students from being able to do their work.
Learning to make simple decisions about this will help them learn to make harder decisions when those times come.