Given that summer abroad programs are becoming more and more popular, the aim of the present study is to find out whether foreign language proficiency can be significantly improved during a summer stay of 3-4 weeks. The present study examines learners' linguistic gains through oral fluency and accuracy measures as well as a listening comprehension task. Learners' oral fluency is examined in terms of syllables per minute, other language word ratio, filled pauses per minute, silent pauses per minute, articulation rate, and length of the longest fluent run. The accuracy of learners' oral production is measured by means of the ratio of error free clauses and the average number of errors per clause. In addition, learners' errors are classified into 4 categories: morphological errors, syntactic errors, lexical errors and covered errors. Results reveal that these short stays do indeed produce significant gains on most measures, and that proficiency level strongly affects the intensity of learners' progress. (Contains 10 tables.)