This study examines out-of-school use of Irish and motivation to learn Irish among final year post-primary students from three different instructional backgrounds: mainstream students studying ordinary and higher level Irish as a subject only and immersion students. Information on motivation and use is linked to student proficiency in Irish. Motivation was measured using items adapted from Gardner's Attitude/Motivation Test Battery and out-of-school use using questionnaire scales. Results show the benefits of out-of-school use for proficiency. There are substantial differences between the three groups on all measures with immersion students having the highest levels of proficiency, motivation and use. As well as the obvious advantage of more target language use within the school, the immersion students also benefit from greater access to Irish-speaking networks outside of school compared to their mainstream peers. It is argued that mainstream students' failure to attain the speaking proficiency levels set in curriculum objectives is due to the limited instructional time in Irish and opportunity to use the language for real communication. This in turn affects personal investment in learning Irish. Ways of increasing student motivation and interactional opportunities, both in school and out of school, are explored.