Not necessarily. Your logic only holds if you assume the "behind" refers to other children.
The statement is ambiguous. I interpret it as "no child left behind THE STANDARD FOR THEIR AGE". In that interpretation, other kids being ahead of that standard doesn't mean the other kids have to be behind the standard. Every kid could be not "left behind" the standard even if some are ahead of the standard.
Of course, NCLB has a lot of other issues, but I think the name isn't the issue.
The statement is ambiguous. I interpret it as "no child left behind THE STANDARD FOR THEIR AGE". In that interpretation, other kids being ahead of that standard doesn't mean the other kids have to be behind the standard. Every kid could be not "left behind" the standard even if some are ahead of the standard.
Of course, NCLB has a lot of other issues, but I think the name isn't the issue.