The aim of this study was to explore learning experience of EFL elementary school students during peer-led English picturebook discussions. This study primarily addressed the following aspects: 1)elements that constituted EFL learners¡¦co-construction in terms of intersubjectivity; 2) the processes of co-construction among EFL learners; 3) the relationships between EFL learners¡¦perceptions of English picturebook discussion experience and their participation in co-construction. The present study adopted a single instrumental case study and recruited four sixth-grade EFL learners in Kaohsiung City. Procedures of data collection included observations and interviews, lasting from June 2009 (excluding July and August) to January 2010. The researcher transcribed the data and employed the constant comparative method for data analysis. In addition, the researcher adopted Matusov¡¦s (1996) idea of intersubjectivity as her analytical framework in the later stage of the data analysis. The study showed the following results. First, the four EFL learners¡¦co-construction constituted both agreements and disagreements. Second, during the processes of meaning co-construction, the four EFL learners drew on single and multiple resources to clarify confusions and extend meanings. Third, during the English picturebook discussions, the four EFL learners¡¦perceptions of peer interaction and participation towards co-construction were mutually affected. The findings of this study are consistent with Matusov¡¦s (1996) concept of intersubjectivity for revealing that some disagreements may encourage co-construction among the four EFL learners. Also, this study echoes Wertsch¡¦s (1979, 1984) idea of situation definition and demonstrates the nature of the four EFL learner¡¦s shifting perceptions when interpreting the activity of English picturebook discussions. For further studies, researchers can explore why some of the disagreements among students cannot encourage co-construction. In addition, future studies can investigate the fluctuating nature of situation definitions and the mutually affected ways of the learners¡¦situation definitions. For EFL elementary teachers who are interested in incorporating English picturebook discussions into peer-led group activities, this study provides two pedagogical implications. First, EFL teachers are encouraged to pay more attention to students¡¦ co-construction processes in peer-led English picturebook discussions, instead of only focusing on the product of co-construction. Second, EFL teachers are suggested to be aware of possible factors that can negatively affect students¡¦willingness to participate in group discussions, such as peer influence and peer pressure.