In this quasi-experimental study, an intervention group (n = 50) of Taiwanese English as a Foreign Language (EFL) 10th graders were given 18 weeks of classroom English reading skill-based instruction in addition to completing homework requiring construction and review of 100 vocabulary word cards for unknown words incidentally encountered during class reading whereas an equivalent Taiwanese EFL control group of 10th graders (n = 50) only received the skill-based instruction. After the intervention, significant differences in second language (L2) reading proficiency and L2 vocabulary acquisition were shown in favor of the intervention group while only a negligible growth in second language vocabulary size was shown for both groups. Additional analyses of the intervention group's L2 vocabulary size data, responses to an open- and closed-ended questionnaire, and the self-constructed word cards revealed anomalies in participants' L2 lexicons, a negative reaction to the technique of using self-constructed word cards for deliberate vocabulary learning, and a need for guidance in selecting target words appropriate for their abilities. Pedagogical implications of these and other nuanced results are discussed.