The effects of frequency, duration, and intensity on L2 learning through Duolingo

Instructed second language (L2) research has frequently addressed the effects of spacing, or, alternatively, the distribution of practice effects. The present study addresses Rogers and Cheungs (2021) concerns about the ecological validity of such work via a natural experiment (Craig et al., 2017). Learners' self-determined exposure and in-app behavior were examined in relation to language gains over time. Duolingo learners of Spanish or French (N=287) completed abackground questionnaire, scales measuring L2 motivation and grit, and two tests of L2 proficiency before and after a six-month period ofuser-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 L2 gains.