Part and parcel of giving short shrift to grammar is dismissing the work of that seminal linguistic grammarian, Noam Chomsky. Chomsky's name is anathema among ABA devotees; Greenspan and his accolytes are merely dismissive. In the Affect Based Language Curriculum, for example, Greenspan writes that Chomsky was wrong to claim that language is innate to the human brain since learning language depends on the social environment.
Anyone familiar with Chomsky will recognize this as a straw man caricature. Of course learning language depends on the social environment. But this does not rule out an innate component, and Greenspan does not address any of the evidence or arguments adduced by Chomsky and others to argue that this innate component exists. Instead, Greenspan goes further, arguing that developing "purposeful affect", or socially-grounded motivation, is all that grammar acquisition depends on:
We create purposeful affect by being a pain in the neck. [E.g. by standing in front of the door the child wants to open.]... We go away a step and come back saying “go, go?”… Once children have that purposeful affect and begin connecting it to the word “go,” guess what they do? They begin using words meaningfully and even using that verb and noun properly.A nonlinguist, Greenspan has no idea how complex grammar is. Neither verb conjugation nor noun phrase formation are trivial, and nowhere in the Affect-Based Language is there any discussion of how to teach this. Instead, as with ABA's Teach Me Language, the entire curriculum is organized around non-grammatical categories: requesting, using words to protest, talking about the past, adding to what the speaker just said.
Meanwhile, I and others have established that there are many children on the autism spectrum who can do all these things with words, but can't speak grammatically. In neglecting grammar, we neglect these children, many of whom are quite capable of learning grammar when it is taught explicitly and systematically.
Why are therapists all across the autism treatment spectrum so dismissive of grammar? Part of it is that their ranks (and the ranks of speech/language therapists more generally) don't include linguists. Here, though, the causality goes in both directions: we linguists haven't exactly been welcomed into the ranks of autism and speech therapists. But their grammar denialism, I believe, extends into the broader population.
Most people think that grammar amounts to learning the labels for word categories (parts of speech), grammar-related spelling distinctions (e.g., "their" vs. "they're"), punctuation (as in run-on sentences), and stylistic rules about dangling modifiers and parallel structure. They have little appreciation for the more basic but complex rules and structure that underlie these rules of style: since the latter rules are innate, we don't need to learn them explicitly, and therefore most of us aren't even aware of them.
Unless, that is, we learn a foreign language grammar whose rules are significantly different from the rules of English grammar. And here is where Americans in particular fall short. If we learn a language at all, it tends to be one whose grammar isn't particularly exotic compared to English, or difficult for English speakers to learn--i.e., French, Spanish, or Chinese. Languages that Americans used to learn, like German, Russian, Latin, and Greek, presented us with far greater grammatical challenges than these languages do--and perhaps with a greater appreciation for grammar than we currently have.
Furthermore, deep appreciation of the grammar of a foreign language depends on in-depth study of that grammar. Most Americans never get to that point. Many abandon their foreign language after a year or two (as in the "world languages" language-surveying model that has become popular in U.S. schools). And, as I discuss in my book, more and more foreign languages classes have reduced grammar instruction to make room for what's called "communicative competence" (which includes conversing in classroom groups, putting on skits, and designing menus, travel brochures, and tissue boxes).
That leaves it up to the linguists of the world to somehow get across to others what grammar really is, and how best to teach it to those who need explicit instruction--be they foreign language learners or children with autism.