Funny, these stereotypes. Everyone has a different idea about what they must wear out of the house to look good, feel comfortable, or seem polished.
I think a lot of it matters what YOU are comfortable with. I'm a preschool teacher and like yourself, it just makes sense for me to dress down for my work. My program focuses on gardening and art and the seasonal world, so I dress for paint and dirt. Think jeans/cords, Keens, a classic tee and a hoodie or sweater. (I eschew the button-down's as well, unless wearing them over a tee and open, more like a jacket.)
What I like to do to 'dress myself up' is to wear a pair of nice earrings. They live in my ears, so I don't have to think about them. Putting my hair back in barrettes is a 'transition ritual' (instead of wearing it down), and necessary as my preschool is in my home. This separates my 'school' days from work days. My earrings and rings are my primary pieces of 'feel-good', because they all have some special, personal significance for me. Other than that, I try to keep the clothes tidy and in good shape.
I did just buy a handbag, too, that I'm looking forward to wearing out and about. Haven't had a 'pretty purse' since heaven knows when. I have a couple go-to sweaters for going out, and a nice pair of Dansko loafers too.
Overall, my style is very laid-back. I live in Portland, OR so I do see those more polished moms when I drop off my son for preschool, but in our town, there's a lot of room for what makes up 'personal style'. I think some people make a choice to get up early and get their hair and face made up. I'd prefer to sleep in, thanks. Plus, my skin is a little oily and doesn't wear makeup well, and after some attempts at trying to wear it, I just stick now to some loose powder (for evenings) and occasional lipstick. . Once I start teaching classes for parents, I'll probably dress up a bit more, otherwise, I love that I can have 'no style' to worry about. Thankfully, the 4 year olds in my group don't really care what I wear, so long as I'm dressed!:)