In my personal experience, I have known many children who returned to school or started school after homeschooling. If the change was child-initiated, the transition generally went very well. If the change was parent-initiated, there was an adjustment period, but within a few months, the children appeared to adjust with no problems. As you may know, on standardized tests, homeschooled children test one year ahead of their schooled peers, on average. By eighth grade, homeschooled children test an average of four years ahead of their schooled peers. This academic advantage does make the transition easier on the child.
I have also seen homeschooled children "try" school. They were intrigued by television shows or books that show happy, smiling kids in the school environment. After a brief period, the reality of school and the hours spent on homework and busywork, negative peer pressure, drugs, and violence (many who wish to try school are teens) cause a change of heart, and these kids return to their former homeschool lifestyle. They appear to be truly grateful to be able to learn in freedom.
If, on the other hand, your question is the transition from homeschool to "public environment", i.e., the "real world", I have to say, there is no transition. Homeschooled kids are out and about in their community every day, going to museums, parks, stores, galleries and shows. They interact with local merchants, relatives, store clerks, librarians, and artists on a daily basis. They develop relationships with kids and senior citizens, and all ages in between. There are no artificial barriers drawn where "learning" should occur. Learning is simply a part of living.