I only had one on my baseball team in the spring, while he was definitely not on the same level as the rest of the team socially, it could have just been that he is a shy kid by nature.
We lived in different countries where people speak a different language, during their earlier years, though, so maybe that also contributes to it.
I can also usually tell just based on the kids if their parents will be helpful or not. If I ask for a parent to help with setting up at the beginning of practice, or if an assistant coach can't make it and I need a hand, the way a kid acts is a pretty good indicator if their parent will get out of their chair on sidelines and come help.
There are outliers, but its a pretty good rule of thumb.
In a positive or negative way?
The benefits of school go beyond what the teachers teach.
They were definitely easy to pick out, but I think in a good way. They were undersocialized with children, but felt way more at ease around adults. They understood more mature humor, spoke larger ideas in better sentences, and behaved perfectly.
And sure, they were a little "weird." As everyone ought to strive to be.