It also depends on your group. If your group is too young it won't make much sense of doing "school theme" based activities or crafts, if you have preschoolers then it is more familiar to them.
I slightly introduce the subject, spark ideas and then go deeper if they're interested. So far, we have been walking and passing by empty schools (I make sure they're aware of that); and when the school starts we go an visit (so they can see how it looks like, who goes there, what teachers do, how children get there, etc).
I create a lot excitement the first days of school (so they are aware of something wonderful happening). We also get familiar with school buses and children travelling.