Duolingo

Spaced repetition

Duolingo is a popular free on-line language learning application. Early in development, Duolingo implemented the Leitner system as a form of rudimentary repetition spacing. In 2016, they opted for their own spaced repetition algorithm, which was a brainchild of Burr Settles. In 2018, for unclear reasons, perhaps in part due to the overly dense repetition schedules, Duolingo dumbed down their application by introducing a Crown system. Perhaps the problem stems from being user-driven? Users always clamor for higher retention, which leads to denser schedules, which leads to more learning pain, and, paradoxically, less satisfaction (see: Stabilization curve). Duolingo was always driven by maximum simplicity to satisfy the widest user base, however, the relegation of spaced repetition met with a protest from users. The official reply was "we are working on it". This sparked the biggest and loudest discussion about spaced repetition that I have ever witnessed. It seems a paradigm shift has indeed happened: spaced repetition is a must in modern learning applications. Disillusioned customers of Duolingo can always give supermemo.com a try.

No pain, no gain

While I admire Duolingo's simplicity and user friendliness, I disagree with some of their philosophy:

Learning a language is a lot like losing weight [...] Just as you need exercise and a healthy diet to get fit, you need to develop a habit of regular study and review in order to stick with learning a language and succeed in the long run. And just as it’s helpful to know what types of foods and exercises are best for staying healthy, it’s important to know what types of learning habits are best for long-term language-learning success

This is reminiscent of my own thinking in the 1980s, or the philosophy behind schooling. Both language learning and dieting can be seen as a struggle (see: Neural network conflict). However, this stands in violation of the Fundamental law of learning. Learning for pleasure and tools like incremental reading are far more efficient than the approach similar to diet-and-exercise. Good habits should be a consequence of the pleasure of learning, not a result of rewards and praise from the teacher (or Duolingo).

When learning is like losing weight, the Crown system is like a sweetener. It is a placebo that substitutes for the actual medicine: happy learning.

In its quest to maximize retention and the addictive component of their system, Duolingo drifts in the same direction as PISA tests. Retention and good grades cannot substitute for a happy mind of an efficient student.

Teaching

Duolingo will reach half a billion users in a not-so-distant future (remarked in late 2018). They can do more good if they depart from the philosophy of teaching, and restore key tools that underlie efficient learning. This includes explicit and easy-to-supervise spaced repetition approach.

Luis von Ahn envisages Duolingo as a supplementary tool in language learning. He believes that software will always struggle in a competition with a good teacher. In his view, teachers excel in their ability to motivate the student. Do we need teachers? If motivation is extrinsic, based on rewards or penalties, it will never lead to high quality knowledge (see: School drive).

Pleasure of learning

For contrast to the philosophy of teaching, compare the philosophy behind incremental reading that relies on the fact that new coherent knowledge sends a reward signal via the learn drive system. This provides for prompt consolidation, good retention, and high applicability of newly acquired knowledge.

See: Pleasure of learning

This glossary entry is used to explain "History of spaced repetition" by Piotr Wozniak (June 2018)