Teachers work hard to teach the children in the classroom, but they aren't the only students. Parents sometimes look at what we do and what the kids do and write it off as "play". And it is, but it is through play that kids learn. Sometimes it is our job to remind parents that.
I found something that might give you the ability to quietly and passively teach parents why we do what we do.
Abcteach.com has a lot of resources for free, some you have to be a member for, but these center signs are free. These signs explain why we play in each center. I put them on poster board, laminate them and put Velcro dots at the bottom for center management.