There has been an ongoing debate on the effectiveness of spaced and massed distribution instruction in second/foreign language learning. A number of studies in the literature have investigated the impacts of spacing effect on English as a Foreign Language (EFL) learners’ vocabulary acquisition. This study aims to expand the body of existing research by exploring the impact of spaced versus massed distribution instruction on EFL learners’ vocabulary recall and retention. To this end, the Oxford Quick Placement Test (OQPT) was administered to 120 Iranian EFL students to determine their level of English proficiency. Accordingly, 75 intermediate students were selected and randomly assigned to three equivalent groups: two experimental groups, namely spaced instruction (n = 25) and massed instruction (n = 25), and one control group (n = 25). After administering a pretest, the participants in both experimental groups received two different modes of instruction. The massed instruction group attended one intensive session to learn each set of target vocabularies; the spaced instruction group, on the contrary, had three sessions at irregular time intervals to learn the same vocabularies. The control group studied the same vocabularies but received no vocabulary-focused instructions. Overall, 180 vocabularies were taught to the students during a 12-week period (15 vocabularies per week). The instructions in each group took 60 min each week. Using a pretest, posttest, and delayed posttest design, the students first took a receptive vocabulary pretest before the treatment. One week after the treatment, a receptive vocabulary posttest was administered. Finally, after a 4-week interval, the students took the delayed posttest. The results revealed that the spaced instruction group significantly outperformed the massed instruction group on both immediate and delayed posttests. The findings lend support to the modulation of spaced instruction into the curricula in instructional settings as a valuable vocabulary instruction technique to promote vocabulary learning in real classroom environments.

关于间隔和集中分布教学在第二语言/外语学习中的有效性一直存在争论。许多文献研究调查了间距效应对英语作为外语 (EFL) 学习者词汇习得的影响。本研究旨在通过探索间隔分布与集中分布教学对 EFL 学习者词汇回忆和保留的影响来扩展现有研究的主体。为此，对 120 名伊朗 EFL 学生进行了牛津快速分级测试 (OQPT)，以确定他们的英语水平。因此，选择了 75 名中级学生并随机分配到三个等效组：两个实验组，即间隔教学（n = 25）和集中教学（n= 25), 一个对照组 ( n= 25）。在进行预测试后，两个实验组的参与者都接受了两种不同的教学模式。集中指导组参加一次集中学习每组目标词汇；相反，间隔教学组以不规则的时间间隔进行三节课来学习相同的词汇。对照组学习相同的词汇，但没有接受以词汇为中心的指令。总体而言，在 12 周内向学生教授了 180 个词汇（每周 15 个词汇）。每组的说明每周需要 60 分钟。使用前测、后测和延迟后测设计，学生在治疗前首先进行了接受性词汇前测。治疗一周后，进行了接受性词汇后测。最后，经过 4 周的间隔，学生们参加了延迟后测。结果显示，间隔教学组在即时和延迟后测中的表现均显着优于集中教学组。研究结果支持将间隔教学调制到教学环境中的课程中，作为一种有价值的词汇教学技术，以促进真实课堂环境中的词汇学习。