>If your kid learns the alphabet at 4 or at 8, what's the difference?
It's a huge difference. As soon as a kid can read, they can learn in a way that isn't just you telling them stuff. They can self-direct their learning, read books about stuff, go online and devour Wikipedia, etc. It's not just "hey, can anyone not read a newspaper by the time they leave school?", it's "how soon does this kid have the tool to satisfy their natural curiosity about things that require more than someone telling them about it?" which establishes their relationship with learning itself, with knowing how to learn.
There is no solid evidence that teaching reading early is advantageous, and in fact there is evidence that it can be damaging. No one really knows why exactly, but there are several theories ranging from discouraging other types of play and interaction, to the difficulty turning them off of reading later on.
>it's "how soon does this kid have the tool to satisfy their natural curiosity about things that require more than someone telling them about it?"
I don't think that's true at all, an average 4-7 year old who can read, cannot read to a level where they can learn topics complex enough that they "require more than someone telling them about it."
A kid who learns to read at 7 will catch up to the kid who learned at 4, so that by the time they are ready to teach themselves on their own through reading, there won't be a difference.
(Personally I was reading by the time I was four without my parents doing anything more than reading to me on a regular basis, and maybe setting a good model by reading a lot themselves.)
In Switzerland age 7 is the standard age to start school. Swiss children are usually doing well enough in international comparisons. Not to say this proves anything, just another data point.
There is a theory that we can read by recognizing the entire shape of a word without processing individual letters within it ("gestalt recognition"). If I understand correctly, this is the same as or similar to the "lexical route" of perceiving words without sounding them out:
I'm pretty sure I learned to read mostly this way, with a big assist from having adults read aloud to me and so memorizing particular stories and then recognizing the appearance of the written words within those stories. Learning about all the letters might have come afterward, and helped me to understand why words are spelled as they are, and also to acquire the "non-lexical route" of systematically sounding out words I didn't know.
Reading acquisition is a pretty complicated process, and I think if we're not teachers or psychologists we might forget that there are so many sub-parts in this process, and that they might also happen in a different order for different children.
I think they're referring to reciting the alphabet. And reading is much more than just "knowing all the letters". It's context, shapes of words themselves, etc.
I'm not an expert on any of these things, mind you. Just that I learnt to speak and read my home-tongue without ever being able to memorize its alphabet. Now that I think about it, I still can't recite it, yet I speak/write the language fluently.
It's a huge difference. As soon as a kid can read, they can learn in a way that isn't just you telling them stuff. They can self-direct their learning, read books about stuff, go online and devour Wikipedia, etc. It's not just "hey, can anyone not read a newspaper by the time they leave school?", it's "how soon does this kid have the tool to satisfy their natural curiosity about things that require more than someone telling them about it?" which establishes their relationship with learning itself, with knowing how to learn.