This study is part of longitudinal research undertaken in 11 secondary schools across two countries, based in Content and Language Integrated Learning (CLIL) classrooms with 12-15 year olds. The aim was to listen to learners, provide them with a "voice" to analyse their perceptions of "successful learning" and to undertake participatory research not only to find evidence of successful learning but also to encourage greater ownership of CLIL classroom events. We believe that this study due to the innovative ways of involving learners has a unique contribution to make to our understanding of "successful learning" using French, German and Spanish in CLIL classrooms where English is the usual medium for learning. For the purposes of this study, "successful learning" was considered to have two components: motivation and achievement or pupil gains. Three distinct data-gathering methods were used: questionnaires, "respectful discussions" and classroom video analysis using the LOCIT (Learning-Oriented Critical Incident Technique) process. The findings reveal that whilst discussing successful CLIL generates useful data to trigger further research by learners and teachers, classroom evidence selected by the learners is less aligned. This study suggests that these data could not only be used to support learners' understanding of "successful learning" more deeply but also to create their own class-based research agendas and to be part of changing classroom practice. (Contains 4 figures.)