This longitudinal mixed-methods study compared the oral fluency of well-educated adult immigrants from Mandarin and Slavic language backgrounds (16 per group) enrolled in introductory English as a second language (ESL) classes. Speech samples were collected over a 2-year period, together with estimates of weekly English use. We also conducted interviews at the last data collection session. The participants' fluency and comprehensibility at three points over 22 months were judged by 33 native speakers of English. We examine the learners' progress in light of their exposure to English outside of their ESL class. The Slavic language speakers showed a small but significant improvement in both fluency and comprehensibility, whereas the Mandarin speakers' performance did not change over 2 years, although both groups started at the same level of oral proficiency. These differences may be attributable in part to degree of exposure to English outside the ESL courses. Neither group had extensive exposure outside of their classes because of employment and familial responsibilities (although the Slavic language speakers reported more opportunities). Thus both groups may have been disadvantaged by a lack of oral fluency instruction. The findings, both quantitative and qualitative, are interpreted using the Willingness to Communicate framework; we also discuss implications for the language classroom.