I've spent a lot of time thinking about why this isn't common knowledge. Why parents aren't told at kindergarten orientation that their child will be tested on writing for the next 13 years but won't be systematically taught it. Why the gap between American and Singaporean writing education doesn't generate the same outrage as math scores.
I think there are two reasons.
The first is that writing is invisible in a way math isn't. A child who can't multiply is visibly behind. A child who writes at half the sophistication of their potential — who submits three sentences when they're capable of a paragraph — looks like they just didn't try hard enough. The gap is attributed to effort, not instruction. Parents are disappointed. Children are blamed. The actual cause — the absence of a system — is never identified.
The second reason is more uncomfortable. Fixing this would require acknowledging that the American approach to writing education — which has been in place for decades and has produced consistently poor results — was wrong. That is a hard thing for any institution to do.
So instead, nothing is said. The scores stay low. The gap persists. And parents who never knew there was a system to look for continue assuming their child's school is delivering one.