The purpose of this study is to analyze the progress of 14 Spanish-speaking learners of English during a period abroad from a longitudinal perspective. Oral and written data were collected three times during an academic year at a British university. These samples were analyzed in terms of fluency, syntactic complexity, lexical richness, and accuracy. The results of the statistical analyses indicate that, while a few months abroad might be sufficient for some gains in oral performance to occur, improvement in written production is slower and does not seem to take place until students have spent more than one semester abroad. In addition, it was observed that the type of interaction experienced abroad and some attitudinal features can partly explain language development in some areas. (Contains 4 tables and 6 figures.)