Despite widespread agreement among ELT researchers that vocabulary lies at the heart of communicative competence, currently no consensus exists as to how learning of previously presented lexical items can be guaranteed. Given the inconclusiveness of findings, the present study attempted to delve into the differences in the learning of target vocabulary through formative assessment. To this end, 58 EFL learners assigned to two groups (the experimental and control group) took a vocabulary pretest. The target vocabulary was explicitly presented to both groups, and the experimental group underwent formative assessment of this vocabulary through such techniques as concept mapping, oral questioning, and vocabulary quizzes. In order to probe deep into the perceptions of formative assessment, two focus-group interviews were held with 14 participants of the experimental group. Finally, both groups sat a posttest whose results revealed that the participants in the experimental group outperformed the control group in terms of vocabulary learning. The findings showed that formative assessment can enable language learners to apply their newly gained lexical knowledge with syntactic correctness and semantic appropriateness. The interviews indicated that participants had a positive attitude toward formative assessment.