The purpose of this study is to examine the effects of out-of-class learning of English by Japanese college students on their proficiency growth measured by the TOEIC test. 809 university students were categorized into three groups by type of learning approach; the 'test-prep' group, who did only test-preparation; the 'general' group, who followed a general type of English learning; and the 'mixed' group, who combined test-preparation and a general type of English learning. The three groups were compared in terms of the changes in their TOEIC scores to examine the effects of different types of out-of-class learning. Using the General Linear Model (GLM), a model was set to predict post-test scores with pre-test scores, study time, type of learning, and the interaction of pre-test scores and type of learning. Results showed that the interaction was significant, which indicates that the effects of different types of learning are moderated by students' proficiency in English.