Interactive digital tools increasingly used for language learning can provide detailed system logs (e.g., number of attempts, responses submitted), and thereby a window into the user's learning processes. To date, SLA researchers have made little use of such data to understand the relationships between learning conditions, processes, and outcomes. To fill this gap, we analyzed and interpreted detailed logs from an ICALL system used in a randomized controlled field study where 205 German learners of English in secondary school received either general or specific corrective feedback on grammar exercises. In addition to explicit pre-/post-test results, we derived 19 learning process variables from the system log. Exploratory factor analysis revealed three latent factors underlying these process variables: effort, accuracy focus, and time on task. Accuracy focus and finish time (a process variable that did not load well on any factors) significantly predicted pre-/post-test gain scores with a medium effect size. We then clustered learners based on their process patterns and found that the specific feedback group tended to demonstrate particular learning processes and that these patterns moderate the advantage of specific feedback. We discuss the implications of analyzing system logs for SLA, CALL, and education researchers and call for more collaboration.