Hard Week for the Dress Dare

So I'm subbing in a special ed class all week - I've been wearing dresses but I have to wear leggings with them cause I never know what will happen with the kids. I'm also having physical therapy on my knees and I shouldn't be wearing the ballet flats, but I can't find comfortable shoes for work and really shouldn't be spending the money. Today the leggings and shoes made my knee throb the whole day and my physical therapist did not appreciate my shoe choice. My husband is encouraging me to wear tennis shoes with my skirts so I'll have a good story (what a good man) - I don't want this school to think I dress crazy... HELP... I really want to give up for just Thursday and Friday while I'm at work...