But they do not use the classical approach. They each have some good books, but overall, to understand the theory of a classical education I think TWTM does the best job of explaining it.
Once someone understands the theory there are tons of websites to help with the nitty gritty of planning and sourcing materials.
I don't think that
The Well Trained Mind does that good a job of explaining the theory. The author's main interest is history (most of her other books are about history) and she ends up promoting a history-heavy curriculum.
If one's goal is imitate the education techniques of the classical period, then the main focus should be language. The trivium part of a classical education - grammar, logic, and rhetoric - is about mastering language. And the ideal language to study, especially for Catholics, is Latin.
While TWTM does recommend Latin materials, it does not make Latin the focus as classical education should. Here is an article on classical education that shows what I mean:
https://www.memoriapress.com/articles/what-classical-education-1/ The liberal arts include grammar, logic, rhetoric, arithmetic, geometry, astronomy, and music. These are the generalizable intellectual skills that you use no matter what subject you are studying or what you do.
The Trivium consists of the first three of these. The first was grammar, which was the study of the structure of language, and this was studied by learning a language (preferably and inflected language—one which required a knowledge of the noun cases) other than your own, usually Latin and Greek. Logic was the study of the structure and rules of rational thought, and this was done by studying the Aristotelian system of traditional logic. Rhetoric was the study of the rules of persuasion, and this was done by focusing on writers such as Aristotle, the great theoretician of rhetoric, Quintilian, the great teacher of rhetoric, and Cicero, the great practitioner of rhetoric. You would also study St. Augustine, who used the skills he learned from these great thinkers to articulate Christian truths.
The Quadrivium (the last four of the seven liberal arts) consists of arithmetic (the study of discrete number), geometry (the study of continuous number), music (the application of discrete number), astronomy (the application of continuous number).
The Trivium consisted of the arts of language, and the Quadrivium, the arts of mathematics. The first was qualitative, and the second quantitative. Together they were considered to equip a thinker to approach any other subject.