It is right in my contract that I encourage kids to get their own clothing on. Here is a bit out of my fall/winter clothing reminder for parents that I just handed out:

Please keep this in mind when buying your child’s winter gear for the season – children’s outerwear should be easy to get on and off. Children aged 3 should be able to put on their own boots, ski-pants, jacket and hat (with a little help from me) and children aged 4 and over should be able to do their own zippers and put on their own mittens. Please buy clothing that is easy for your child and practice letting the kids dress themselves at home.