The greatest advantage of long form reading, both fiction and non-fiction, is it scales up our ability to internally and intensely world-build and cathedral-of-concepts build at high scale, high density and at a high resolution of relationships and/or facts.
Our imaginations and reasoning become capable of accreting and operating over much larger internal structures deeply and coherently, in the day to week time range.
The only other equivalent I can think of in terms of both scale and detail, are major areas of study, which we develop over years or a lifetime, or large engineering projects, such as a large architectural of software project, which we develop over months or a few years.
The much faster cadence of books on a daily or weekly basis is an incredible mental workout we can carry on our whole lives. And great preparation and maintenance, for being able to think at both the highest scales and resolutions.
I have seen children that got read to every night, when they were tiny, and went on to become avid readers as adults. And children in the same cohort that didn't, who find reading a book very challenging as adults. They are all grown up intelligent, curious, with good jobs, and still know each other. But there is a marked difference in their abilities to think about the world, and the scale of their thinking and interests.
Since these children were in a cohort, and still know each other, it is telling that the children that didn't learn to read and enjoy book length reading early in life, are well aware of that difference within the group, and have expressed the wish that they would have had more early exposure to reading books.
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For myself, I was read to as a tot, and then very socially isolated for most of my childhood, with the result that I learned to read voraciously for decades. And would go to great lengths to find ways to earn money to buy books.
But even I have a harder time now. There are a lot of insightful and quality blogs and articles to read on the internet, but after that displaced a lot of long book reading, I have noticed the latter presents a greater challenge for me. That it presents a challenge at all is a significant change.
Contrary to that, reading formal papers seems to be a great challenge for my mind, in terms of keeping it sharp. A lot of papers require a high intensity of thinking to fully understand.
Which strikes me as interesting, and perhaps an untapped opportunity for young readers. I don't know what the young reader fiction or non-fiction equivalent of a formal paper would be. But perhaps a short story mystery or intense subject dive, that required the reader to solve or apply the knowledge in some way would be an interesting format for children. Higher scale puzzle solving, in short form reading format.
Perhaps dense essays for children, but highly vetted/curated for being of of genuine natural interest to children. Across a very wide variety of areas, so children have great freedom to pursue their own interests without being pushed or funneled. Traditional childhood subjects of spontaneous study, like dinosaurs, cosmology, animals, cultures, ancient history, how to make things, would all be good areas.
I love the idea of having a recognizable format for these essays that somewhat mimics formal papers aesthetically. Gives the children a clear aesthetic signal of what is an intense "chapter sized book", vs. a regular book or other type of reading. And makes the adult activity of learning at the frontier, feel familiar to them very early on.
I believe a lot of ways children's potential is wasted is simply not introducing little bits of downstream patterns and aesthetics earlier. Children have an incredible ability to absorb simpler forms of complex "adult brain" subjects early. And when they do, they find the latter much less challenging and more interesting when they eventually encounter them in their full complex/challenging form. Simple feelings of familiarity are so helpful to us emotionally when we encounter a new challenges.