He’s right about one thing: the skills tested under “grammar” aren’t all grammar, and it would be more accurate to call it the “spelling, punctuation, grammar, vocabulary and register” test. But that might be a bit much of a mouthful for 10-year-olds. Plus, as he correctly says elsewhere in the post, words have different senses and connotations, and it can be unnecessarily limiting to restrict yourself to just one sense of a word. “Grammar” has a technical sense (syntax and morphology) and a broader colloquial sense that also includes vocabulary and register.

Some people (like me, and presumably like Rosen based on the fluency of his writing) find this stuff (“grammar” in the broader sense) fairly intuitive: we derived it by reading widely for pleasure and by automatically, unconsciously applying an analytical mind to infer the patterns from the data. But many people don’t have all those privileges: they may lack one or more out of the analytical mind, the incination to read widely, or the opportunity to read widely. It’s remarkable what sort of nonsensical word soup they can produce as a result. If they’re going to understand language that they have to read in the context of household admin or employment, if they want to express themselves and be understood, if they want to sound intelligent and be taken seriously, they need to be taught this stuff explicitly. Wanting to prevent that smacks of pulling the ladder up behind oneself.