Why do head-to-head quiz "duels" work so well as a learning tool?

They force rapid, repeated retrieval under mild time pressure with immediate feedback — a compact package of everything that makes testing effective.

A duel isn't just a game; it's engineered retrieval practice:

• Retrieval: each question makes you pull the answer, not recognize a re-read page.
• Repeated & rapid: many questions in quick succession means many retrieval events.
• Mild time pressure: a little arousal keeps you engaged and blocks passive coasting.
• Immediate feedback: you see the right answer at once, so errors get corrected, not consolidated.

The competition is motivational scaffolding wrapped around the mechanism the evidence actually supports.