Abstract
Spacing and repetition are two fundamental principles of learning, yet under limited instructional time, increasing repetitions necessarily shortens the intervals between encounters. Prior research found that more repetitions with shorter spacing produced better learning than fewer repetitions with longer spacing, but the respective contributions of spacing and repetition remained unclear. The present study sought to disentangle these contributions and replicate prior findings. Data were collected in 2026 from 120 English-speaking U.S. adults. Participants learned Indonesian-English word pairs three or six times under both massed and spaced schedules within a fixed instructional time. Retention was assessed immediately, one day, and three days later, and forgetting curves were used to estimate initial memory strength and forgetting rate. We replicated the advantage of more repetitions with shorter spacing. Spaced practice produced greater initial memory strength and slower forgetting than massed practice, whereas additional repetitions increased initial memory strength only when practice was spaced. These findings suggest that, under time constraints, additional repetitions benefit learning primarily when spaced, indicating that the advantage of repeated practice depends on the accumulation of learning across spaced encounters.