On one hand, summer seems to be dragging on and you are looking forward to school starting again. Yet, your toddler spent the first three weeks of school last year feeling anxious and crying and you can't stomach the thought of going through that again. There are things you can do now to help prepare your little one to make the transition easier.
For starters, go visit school. If there's a summer camp program there, even better. Choose a time when kids will be on the playground and take your child to see how much fun they are having. If possible, ask the Preschool Director if she can tell you who your child's teacher will be, and if that teacher is there in the summer, take your child in to meet her. If not, let him bring cookies or flowers into the secretary or gym teacher or someone else who will be a familiar face come September. It's all about making him feel comfortable.
Then, give him something to be excited about. If you know the classroom he will be in, take him in to see it. Find a specific toy, stuffed animal, poster, or some object that he is attracted to, and give it a special name. Find something about that object that you and he can have a "secret" about, and remind him that you can't wait until he gets to school so he can see it again.
Go shopping and choose a backpack with your child's favorite character on it that he will be proud to show off in school. Let him pick it out (if you are worried about his selection, give him two choices that you approve, but let him decide which one.) Do the same for his back to school outfit. The night before school starts, lay his clothes out (that he has chosen) and encourage him to dress himself in his special new duds.
The more your child feels that he is part of the process, the more comfortable he will feel, and the easier his transition will be.