Undesirable Difficulty of Interleaved Practice: The Importance of Initial Blocked Practice for Declarative Knowledge Development in Low‐Achieving Adolescents

This study explored the effects of practice schedule on the processing of new second language (L2) vocabulary and resulting knowledge. Participants were 107 low‐achieving adolescents attending a vocational high school in Korea. They were randomly assigned to one of three practice groups and completed a L2 English–L1 Korean paired‐associates learning task. The blocking group practiced one word at a time before switching to different words (e.g., A/A/A/B/B/B/C/C/C); the interleaving group practiced multiple words in sequence (e.g., A/B/C/A/B/C/A/B/C); and the hybrid group had both blocked and interleaved practice. Results revealed that (a) interleaved practice alone posed undesirable difficulty for low achievers, (b) blocked practice in the early learning phase facilitated the development of new declarative knowledge, and (c) hybrid practice produced more robust long‐term retention than blocking and interleaving. The findings are discussed in relation to real‐time processing accuracy, reaction time, coefficient of variation, and meaning recognition test outcomes. Additionally, I explore possible applications of these findings in developing optimal algorithm‐based software for vocabulary learning.