Lexical inferencing has not led to substantial vocabulary gains. In previous studies, the learners were not obliged by design to notice the unfamiliar words and static approaches to assessment were adopted. In this quasi-experimental study, we adopted dynamic assessment (DA) approach and took measures to ensure noticing of the new words. Through purposive sampling, 80 intermediate English as a Foreign Language (EFL) students were selected as participants. They were randomly assigned to computerized dynamic assessment (CDA) and static assessment (SA) groups. Participants read five texts, one per week, and inferred the meaning of highlighted unfamiliar words. In CDA group, through a software program, struggling learners received graduated mediational hints for each target word which helped them to infer the meaning of unfamiliar words. No mediational assistance was provided to the participants of SA group. Acquisition and retention post-tests were administered to both groups one day and four weeks after reading each text, respectively. Results showed that vocabulary gains in CDA group were significantly higher than those in the control group. The findings suggest that the noticing of unfamiliar words and the adoption of DA approach could enhance vocabulary gains from lexical inferencing.