> I'd like to add that educational psychology is just a grab-bag of weak correlations whose discovery was [un]motivated

That's not just educational psychology. All of child psychology and child development is like that. People still talk as if Piaget might have been on to something.

Note that while the article doesn't really provide anything convincing, there is good reason to believe that indicating prosody makes it easier for children to understand written text.

The argument is just that, despite the writing system making absolutely no provision for any indication of prosody, native speakers keep spontaneously adding such indications to their writing. Look at this sidethread comment:

> A school my wife used to work at is requiring all 8th graders to take algebra (normally a high-school-level class in the US) regardless of math aptitude because some study shows that 8th graders who take algebra have improved outcomes. [italics show prosody]

> Nevermind the fact that this is almost certainly because kids who are already good at math will both take algebra AND have improved outcomes. [italics show prosody, and since that wasn't enough here, capitalization does too]

Or here's the New York Times in 1993:

> I used to speak in a regular voice. I was able to assert, demand, question. Then I started teaching. At a university? And my students had this rising intonation thing? It was particularly noticeable on telephone messages. "Hello? Professor Gorman? This is Albert? From feature writing?" [question marks show prosody]

( https://www.nytimes.com/1993/08/15/magazine/on-language-like... )

If it's important enough that everyone feels the need to write it down even though they aren't supposed to, it's probably important to children too.