The purpose of this intervention study is to reveal the extent to which memory-related aptitudes are implicated in the second language (L2) fluency development fostered by task repetition. English L2 learners are engaged in oral narrative tasks three times per day under two different 3-day task repetition schedules: blocked (Day 1: A-A-A, Day 2: B-B-B, Day 3: C-C-C) versus interleaved (Day 1: A-B-C, Day 2: A-B-C, Day 3: A-B-C). Their phonological short-term memory (PSTM), attention control, and associative memory were used as predictors of fluency changes measured through speed, breakdown, and repair fluency behaviors. Results showed that while the articulation rate change was not explained by any of the examined predictors, breakdown and repair fluency were predicted by different memory components. Specifically, PSTM was associated with mid-clause pause decrease during the training phase, while associative memory was linked to the increase in clause-final pauses in the posttest. Attention control, as well as PSTM, was related to greater repair frequency in the posttest, indicating increased learners’ attention to speech monitoring. Furthermore, PSTM and associative memory contributed to reducing breakdown fluency in the blocked repetition condition only, suggesting that learners can capitalize on their memory for improving oral fluency by engaging in blocked practice.