Many parents believe that boys develop motor skills before language whereas girls develop language skills and lag behind on motor development. Think of all the different possibilities when you expand your understanding in terms of this wider arena of development. It's easy to imagine a child who is working toward expressing his social skills and motor skills while lagging behind on intellectual skills or vice versa. In addition it would be predictable that if a child had to cope with any stressor -- including a family crisis, a health crisis, even just changing schools or grades -- that anyone of these developmental tasks could be put on hold while the child simply coped with the change he or she was facing.
Sometimes what looks like a disorder is a failure of patience. I have had clients who presented with intense worry and concern about a child in one arena who felt pressured by teachers or pediatricians to try medications. In some of these cases, when the parents just waited the problem would resolve itself over a year or two.