There is an old finding that survives every replication fight: explaining something is a brutally honest test of whether you understand it. Reading feels like knowing. Explaining exposes the seams. TeachBack, live for everyone today, is that test as a tutor mode.
How it works
Pick a concept and explain it — as if to a classmate who missed the lecture. Sapling maps your explanation against the concept’s actual pieces and comes back with a verdict per piece: what you covered correctly, what stayed vague, and what went missing entirely. Explaining an AVL rotation, you might nail the direction, wave at subtree reattachment, and skip which node becomes the new root. It will tell you exactly that, and then ask you to re-explain.
Mastery moves on the result — and yes, it can move down. If your explanation reveals a gap the graph did not know about, the honest response is a lower score and a review card, not a participation trophy. A gap found in TeachBack is a gap that will not find you in the exam.
TeachBack joins Socratic and Expository as the third way to work with the tutor. Same graph, same grounding in your course materials, opposite direction of travel: this time, you are the one doing the teaching. It is the mode we use most ourselves, and the fastest one at turning "I read it" into "I know it."