> ## Documentation Index
> Fetch the complete documentation index at: https://docs.timeback.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Learning science

> The hierarchy of learning mechanisms that guide Timeback's design

Not all learning mechanisms are equal. Research and implementation reveal a clear hierarchy that guides every design decision.

## Tier 0: Non-negotiables

These must be in place before anything else matters.

| Mechanism                   | What it means                                                                            |
| --------------------------- | ---------------------------------------------------------------------------------------- |
| **Faultless communication** | Instruction is unambiguous. Examples clearly distinguish what counts from what does not. |
| **Retrieval practice**      | Active recall is the primary learning event, not passive consumption.                    |
| **Mastery gating**          | Students do not progress without demonstrating ≥90% accuracy on rigorous assessments.    |

## Tier 1: Force multipliers

These amplify Tier 0 once the foundation is solid.

| Mechanism           | What it means                                                          |
| ------------------- | ---------------------------------------------------------------------- |
| **Spacing**         | Distribute practice over time. Cramming creates temporary performance. |
| **Interleaving**    | Mix problem types to prevent context-dependency.                       |
| **Worked examples** | Study complete solutions before attempting problems.                   |
| **Feedback**        | Immediate for basic facts; elaborated (explaining why) for concepts.   |

## Tier 2: Context-dependent

These work under specific conditions.

| Mechanism        | What it means                                                                     |
| ---------------- | --------------------------------------------------------------------------------- |
| **Novelty**      | Activates attention. Useful for marking practice intervals.                       |
| **Multimedia**   | Combine verbal and visual when both add value. Avoid redundancy.                  |
| **Gamification** | Can increase engagement if it reinforces learning behaviors, not just completion. |

<Tip>
  Tier 0 is binary. You either have faultless communication, retrieval practice, and mastery
  gating, or you do not. No amount of Tier 1 or 2 optimizations can compensate for a broken
  foundation.
</Tip>