In sixth grade, it's usually pretty easy to separate the "get-it"s from the clueless. Some kids are really capable of higher order thinking, and they definitely stand out from those who aren't quite there, yet. The thing is that people's brain's develop a lot like we grow-- the tallest kid in the class this year may not tower over the crowd in seventh grade. We expect such diversity of development in kids when it's physical, but it's much harder to accept differences in cognitive and emotional growth, perhaps because they are so intangible. Even so, the kid who doesn't grasp a tough concept today in a few years may be able to completely out-think the one who does.
It's important to keep this in mind, because so often the early cognitive bloomers get labeled as smarter than their peers and thus are treated differently, as are the seemingly less intelligent students in the group. There are obvious benefits of being treated like you're smart-- in general, you are asked to attempt more complex tasks and are supported by the confidence of those around you that you are capable of them. More importantly, though, at this age, kids are beginning to form self-concepts, and how the adults in their lives see them is crucial to their opinions of themselves.
As an example, think about how hard it is for people in a family to shed the identities that they acquired as they were growing up-- the responsible, hard-working sibling can rarely do wrong, while the screw-up can rarely earn redemption. Such roles are usually self-fulfilling and self-perpetuating.
For most eleven-year-old kids anything can happen, and it's up to us to make sure that stays true.