Many of us probably struggle a bit with sending kids to public school after they have been homeschooled. For me personally I wanted my kids to have access to certain programs that the schools offer that I can't find anywhere else.
My oldest son is now a sophomore and his biggest issue when faced with entering public school for the first time last year was that he was worried that he would not be academically prepared. In about two days his mind was at rest and he knew he was fine. He felt socially up to par as he had gone to various churches with the same kids at the school, he has been in scouts with them and he has played little league for years with the same kids so he had built in friends and familiar faces. This boy can challenge any one's idea that he wasn't socialized properly. He is on the honor roll, still plays baseball and is on the cross country team as well as drama club and FBLA. I am not bragging, I am just saying that he came out of the homeschool setting as a self motivated young man with goals and ambition!
My other son just entered public school for his freshman year. Because of the example set by his brother he felt completely at ease (well, with excitement) with going to the building each day.
Both of my boys have opted to do a duel enrollment where they take BYU Independent Study courses through our school district. They are both doing their math and their English at home online. They love having the luxury of leaving school early and not having the amount of homework that other kids have. The online classes are challenging for them but I think that is good! And they will be receiving college credit as well as high school credit so it just doesn't get any better than that! Free college credits!!!
Basically, if you have done your work with your child when homeschooling and you have kept them up to grade level or beyond as well as getting them into the community your child will transition fine. With that said, my only experience has been for the high school age. I am not sure how it goes in elementary schools. I think my younger two would have a hard time. Mainly my first grader. She has some learning issues and she would probably benefit from classroom management but it would be awful for her and the teacher right this moment. So, I will work with her at home and only send her if I feel the benefits out weigh homeschooling.
If you have had an experience with this kind of transition please share. It is always good to hear from others and to learn from them.