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language gains over time. Duolingo learners of Spanish or French (N = 287) completed a background questionnaire,
scales measuring L2 motivation and grit, and two tests of L2 proficiency before and after a six-month period of user-controlled
app usage. Total minutes of app exposure exhibited a correlation with written but not oral proficiency gains. More dependable
correlates of gains were frequency- and curriculum-oriented measures. Additionally, L2 grit and motivation were weakly to
moderately correlated with several in-app behaviors. We conclude with implications for how apps can best be leveraged to produce
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