The effectiveness of different teaching methods of collocational expressions in ESL/EFL contexts of education has been a point of debate for more than two decades, with some believing in explicit and the others in implicit instruction of collocations. In this regard, the present study aimed at finding about which kind of instruction is more rewarding for Iranian pre-university students in Iran. To this end, 90 pre-university students were randomly distributed into three groups, explicit instruction, implicit exposure, and control group with each containing 15 female and 15 male students. All the groups participated in preparatory classes which lasted for 8 weeks, 16 sessions for each class. The participants were then given three sets of multiple choice questions as pretest, posttest, and delayed posttest. The results of data analysis indicated that both implicit and explicit method of teaching collocations were effective with regard to their efficiency in development of collocational knowledge in both posttest and delayed posttest. However, the explicit group outperformed the implicit group in both posttest and delayed posttest. The findings of the study can be illuminating for all those who are teaching English in both formal and informal context of education in Iran.