This study reports the findings of a classroom intervention experiment investigating the effectiveness of explicit instruction in teaching the English articles’ semantic properties (definiteness and specificity) to Hejazi Arabic-speaking learners. Additionally, the study explores whether learners fluctuate (use the instead of a/ an and vice versa) in contexts where the taught semantic properties do not match. Fifty-four Hejazi Arabic-speaking participants were divided into two groups (instructed and control/uninstructed). The instructed group received explicit instruction on specificity and definiteness, since specificity is currently not taught to learners of English whereas definiteness is. The control group received traditional English language lessons with no explicit instruction on article semantics. By comparing the participants’ performance with twenty-three native English speakers, the findings of the study show learners’ sensitivity to specificity in article choice. They further show evidence supporting explicit instruction. The instructed group outperformed the uninstructed group and this effect was sustained until the delayed post-test with respect to average effects. The paper concludes that generative linguistics can inform the language classroom by predicting areas of acquisition difficulty. It also stresses that explicit language instruction is more beneficial than standard classroom instruction in teaching articles. On the basis of the findings, theoretical and pedagogical implications are discussed.