The present study aimed to investigate the effect of learning context on the acquisition of plurality agreement in English noun phrases by Iranian L3 learners of English. To this end, 64 elementary learners of English were chosen from among the students of Arabic language and literature and Persian language and literature of Ahvaz university and Yazd university via the Oxford Quick Placement test. The participants were assigned to four groups to be compared in terms of the comprehension and production of plurality agreement via a grammaticality judgment correction task and a picture description task. The first and the second groups had Persian as their first language (L1) and Arabic as their second language (L2) but differed from each other concerning their language of contact instruction, Persian and Arabic, respectively. The third and fourth groups had Arabic as the L1 and Persian as the L2 but differed from each other concerning their language of contact instruction, Persian and Arabic, respectively. The results showed that the groups which had Arabic as their language of contact instruction outperformed the other groups in both tasks, which suggests that they transferred plurality agreement facilitatively from Arabic, which was their language of contact instruction. Therefore, the results of this study suggest that the context of learning matters in the acquisition of L3 properties since the L3 learners associate their language of contact instruction with the L3 in their mind due to the similarities in the learning context.