Textbooks are limited to conveying information and providing exercises. The two would suffice to teach machines (who only need information) and animals (who only need training exercises), but they are extremely limited resources for teaching human beings, who can’t learn anything worth learning without being puzzled, challenged, and generally confused in an appropriate way. One can’t do without long lists of Algebra problems, distilled-out facts, and various other drills, but even a perfect facility with all these is more a preparation for thought than actual human thought.
Textbooks try to remedy their shortcomings with flashy pictures that are intended to generate interest (Look! a skateboarder leaping above the
Communitive Commutitive Property!) but the student treats them as background noise. Textbook chapters might begin with pointed questions that are intended to generate interest, but the student knows to read past them to the part that tells him what to think. Textbook readings may end with questions, but they are not the questions any first time reader asks. They are too leading and too reflective while actual student questions are ill-formed, confused, and tied to random things that student happen to be interested in or confronted with that day. Still, one has to start with the actual questions of a first time reader. You can’t educate someone by raising the sort of questions that are addressed to an educated person.
There is also a subtle but infinite difference between speaking down to a student and starting with the simplest and first questions of a discourse. The first is simply a dumbed-down report that puts the discourse at a distance; the second is an articulation of the discourse itself. There is a vast difference between taking the science to the student (i.e. knocking it down a peg to the point where people can get it) and taking the student to the science (i.e. doing the science itself with an eye to the parts of it that actually are capable of generating interest of themselves). The Euthyphro or the Confessions are beginner texts, but they never break the fourth wall to address themselves to the learner, who can simply look in on them to see a real discourse being carried on.
One might object that the whole point of the teacher is to remedy the limitations of the textbook. This is fine as far as it goes, but part of this remedy is making the textbook and instrument or auxiliary to the teacher. The teacher is not some tutor of textbook discourse – it’s completely the reverse.