The present study investigates the differential effects of explicit and implicit feedback on L2 learners at different proficiency levels as measured by L2 development and learner uptake, which is defined as the learner's responses following feedback. Twenty-three learners of Chinese as a foreign language at two different levels of proficiency at a large Mid-western university in the United States participated in the study. Participants from each of the two proficiency levels were randomly assigned to either the explicit or implicit group. The learners received either explicit or implicit feedback on their erroneous production of Chinese classifiers while engaging in communicative tasks. Independent variables included feedback type, proficiency, and time. Dependent variables included the learner's performance scores on classifier use and learner uptake. Results revealed that for low-proficiency learners, explicit feedback worked better, but for high-proficiency learners, the explicitness of feedback did not make a difference. It was also found that overall the uptake level was high (nearly 100%), implying that uptake is limited as a reliable index of L2 development in this context. (Contains 4 tables, 1 figure and 6 notes.)