Do you think asynchrony can exist in typical kids with an average IQ where they can be advanced cognitively (specifically in terms of early reading, spelling and puzzles) but a little behind socially and physically during early childhood, but even out later? Does asynchrony necessarily mean anything or is this a variant of developmental trajectories that often doesn't have to be tied to an outcome like ASD or high IQ?

I think that it depends on what you mean by "asynchrony" in this context.

Yes, I'd say that temporary areas of asynchrony may definitely occur in the NT population. But they tend to be transient and still well within the central 2 standard deviations from the mean.

So if child is at the 50th percentile for everything else, maybe is a bit klutzy for a period of 18 months or so starting kindergarten... that particular domain (large motor) might be at the 15th percentile for a while. So sure, there's an asynchronous gap, but it's not really diagnosable, it's not long-standing or persistent, and it's never extreme.

Does that explain it? I think it becomes "asynchrony" in the sense that we're used to using that term when the child in question has a really substantial gap in between developmental domains, no matter what those might be.

At that point, this is pretty much what it means to be "gifted" in the functional sense.

Can anyone give me book or article recommendations that discuss asynchronous development?

Through which lens?

Asynchrony as pathology, or when-to-be-worried?

Or asynchrony as "normal" for some people, or the pragmatic outlook that thinks it is what it is and that probably coping skills are all that is needed?

For the latter, just using "asynchrony" as a search term at Davidson, SENG, and Hoagies should get a lot of material.

For the former, hopefully someone else will have some good suggestions.

A certain amount of asynchrony is normal in the sense that everyone will develop faster in some ways than others. It's a question of degree.