Ask a student where they lost the thread in a maths lesson and they rarely point at a word. They point at a moment: the line where two things were happening at once and only one of them was said out loud.
The dual-channel problem
Working memory processes visual and verbal information through separate channels. When an explanation is entirely verbal, one channel does all the work while the other sits idle, and the diagram the student needs gets built, badly, in their head.
This is the core of Mayer's multimedia principle: people learn more deeply from words and pictures together than from words alone. Not from prettier words. From pictures, arriving at the same time as the words that describe them.
Why a static diagram isn't enough
Textbooks have diagrams. They arrive finished. The student sees the destination without the route, which hides exactly the part they needed: the order things were constructed in.
- A finished triangle hides which side was labelled first, and why that choice mattered.
- A completed derivation hides the moment a substitution was chosen over expansion.
- A final graph hides which feature was plotted from the equation and which was inferred.
“The value isn't the diagram. It's watching the diagram get built.”
What we built instead
Santi Tutor renders every lesson as timed strokes on a board. The tutor writes the statement, sketches the triangle, labels one side, pauses, then labels the next, and the narration is locked to the stroke that's happening.
Because the board is a timeline rather than an image, you can scrub it. A student who lost the thread at step three drags back to step three instead of re-reading the whole thing.
The measurable difference
In our pilot with 40 students across maths and physics, the topics taught on the board produced noticeably fewer repeat questions than the same topics taught as text. And when students did come back, they came back with a sharper question about a specific step rather than "I don't understand this topic".
Want to see this in practice?
The board is the whole argument. Watch a lesson, or join the waitlist and bring the topic you're stuck on.