This study investigates the effect of applying the Comprehension approach in classroom instruction of Indonesian as a foreign language. The comprehension approach, also known as the input based approach, claims that for acquisition to take place there must be a period of time allowed to process input without any pressure to produce. In other words, instruction will be more effective if it is based on input rather than output practice. Most Indonesian language training, especially during the beginning stage of acquisition, has ignored this input based approach, emphasizing the output or production approach. This study compares two different interventions at the elementary level of the acquisition of Indonesian as a foreign language: one that is based on the comprehension approach, the other on the production approach. Students enrolled in two semesters of elementary Indonesian courses- a total of 200 students in semester one, and 58 in semester two-were divided into input and output groups, both of which were taught using equal amounts of time and materials by the same team of teachers. Students' language acquisition was measured based on the post and delayed post tests used to evaluate students' performance in comprehension, as well as production tasks. These tests were administered at the beginning, middle and end of each semester. In addition, an oral interview was administered at the end of each term. The findings from the first semester of study indicated that the input group students outperformed the output group students on the comprehension tasks, and performed as well as the output group on the production tasks. However, in the second semester of study it was found that there were no significant differences between the input and output groups on comprehension and written production tasks, although the output group outperformed the input group on oral production tasks. The results of this study suggest that focusing on comprehension input activities works very well in the early stages of Indonesian acquisition in developing comprehension and production skills. However, prolonged focus on comprehension activities may not be as beneficial in developing optimal oral production skills, as learners fail to benefit from the opportunity to experience pushed output in comparison to the output group. On the other hand, production training may develop comprehension as effectively as written-cum-oral production skills in the long run, although a focus on production activities at the early stage of acquisition seems to impede the development of comprehension skills. While the present study supports the assertion that input is paramount in facilitating acquisition, the results also indicate that at a later stage output plays a significant role in enhancing acquisition.