This investigative inquiry explored the role of cognitive aptitudes in defining the effect of practice distribution on second language learning. The inquiry examined to what degree language-analytic capacity and working-memory ability predicted grammar acquisition under two learning conditions that diverge in the interval between the two training sessions. Learners of Japanese as a second language were trained on an element of Japanese morphosyntax under either distributed practice (7-day interval) or massed practice (1-day interval). The results disclosed that language-analytic capacity was only linked to performance after distributed practice, whereas working-memory ability was only linked to performance after massed practice. These Aptitude × Treatment interaction findings can aid initiate the learning processes operating under distributed/massed practice conditions.