Spacing is a crucial factor in foreign language word pair learning. However, findings regarding optimal spacing in this domain have been inconsistent. Therefore, adopting a treatment-immediate-delayed post-test design, the current study investigated the optimal spacing for both receptive and productive word knowledge across different test timings during foreign language word pair learning. A convenience sampling method was used to recruit 152 pre-intermediate English learners to participate in this study. The study manipulated spacing schedules (equal, expanded, and contracting) and examined their effects on receptive and productive word knowledge in immediate and delayed post-tests. The results revealed an advantage for contracting spacing for both receptive and productive word knowledge in the immediate post-test. However, for productive word knowledge, an advantage for expanded spacing emerged in the delayed post-test. The present study proposes a hybrid optimal spacing system that dynamically adapts spacing strategies based on the type of word knowledge. This system suggests using contracting spacing for short-term retention of receptive word knowledge and transitioning to expanded spacing for long-term retention of productive word knowledge in foreign language vocabulary learning, teaching, and software design. The findings support and extend the retrieval effort hypothesis, the desirable difficulties theory, and the encoding variability theory.
Kang Zhai (2026) studied this question.