> dating back to the Middle Ages Or realistically long before the invention of writing. Observing the world together and explaining what is happening is one of

> dating back to the Middle Ages Or realistically long before the invention of writing. Observing the world together and explaining what is happening is one of the things parents do with their young children all the time, and is also a big part of how tutoring/coaching/mentoring works in any field, and arguably a focus of good lectures as well. Legibly adding layers of commentary in written books is a difficult typographical challenge though. Medieval-style books aren’t all that easy to read. The biggest problem by far with many current textbooks, at least in early grades, is that they are developed by people without any particular skill or expertise, based on a terrible committee process driven largely by politics and marketing. I don’t think adding interlinear annotations would help.