This paper reports the results of a mixed-method study which was conducted to investigate whether Malay ESL learners who were, at the time the study was conducted, first-year Diploma in Computer Science students in a public university in Malaysia could improve their receptive vocabulary knowledge incidentally while reading silently in the classroom. A quasi experiment and a focus group interview were used to collect quantitative and qualitative data, respectively. The following were the two main research questions of the study: a) What is the effect of focused in-class reading with writing activity on the students' receptive vocabulary knowledge at the 2,000 word-family level? b) What are the students' perceptions of these activities in improving their vocabulary knowledge? The study concluded that a short period of focused in-class reading and writing activity conducted consistently can improve L2 learners' receptive vocabulary knowledge. Although both the experimental and control groups showed significant improvement in their receptive vocabulary knowledge at the 2000-word level, the vocabulary growth for the experimental group was higher than for the control group. In addition, the participants perceived focused in-class reading with writing activity as beneficial in improving their general vocabulary knowledge.