Recent research on English as a foreign language (EFL) vocabulary instruction has surged due to its inherent importance and the challenge it poses, given the vast number of words in languages. Many studies explored how reading enhances EFL students' vocabulary. However, empirical studies on how narrow reading aids beginners' vocabulary growth are lacking. Hence, this study purports to investigate the impact of narrow reading on the development of Moroccan EFL students' receptive vocabulary knowledge. An experimental pretest post-test design is adopted. 75 10th grade (common core) beginner students belonging to three groups participated in the study. The first experimental group read 4 texts on the same theme and written by the same author. The second experimental group read 4 texts written by the same author. The control group read 4 texts written by different authors on different themes. Meara's yes/no test was used to measure the participants' receptive vocabulary knowledge before the treatment. The treatment lasted seven weeks. The vocabulary knowledge scale (VKS) was used to measure students' receptive vocabulary gains. The results of a one-way ANOVA showed that the group which read texts on the same theme and by the same author outperformed the other groups. Informal discussion with the participants unveiled some factors that have eased vocabulary uptake.