Duolingo tries to do some spaced repetition, but it’s not very effective. Spaced repetition should be at least explicitly memorizing the definition of vocabular

Duolingo tries to do some spaced repetition, but it’s not very effective. Spaced repetition should be at least explicitly memorizing the definition of vocabulary (and related uses) with a smart algorithm while Duolingo only exposes you to words occasionally, in the form of sentences.