What is the role of positive feedback in the adult English language classroom? This study applies ideas from complexity theory to explore the relation between frequency of oral feedback received and student language proficiency. The researcher collected data from digital recordings of adult students (N = 41) who attended classes for 30 weeks at Portland State University Laboratory School. During the focused observation, the researcher recorded tokens of praise, affirmation, laughter, and nodding given by teachers and students in response to target student interlanguage. Students provide far more affirmation tokens than praise tokens to their peers, while teachers issue each with nearly equal frequency. Statistical tests support the hypothesis that the rate of positive feedback received is associated with ESL student course level promotion regardless of student variables such as initial course level, gender, and first language (L1). The results support a possible language learning model akin to the complexity theory notion of increasing returns: Minor initial gains in producing English can result in more rapid second language development, the gains building on one another to form a positive feedback loop. (Contains 1 figure and 3 tables.)