Although many second language (L2) teachers identify motivating their students as an important challenge, few education programs focus on raising pre-service teachers’ awareness of the role that motivation plays in L2 learning. There is little consideration of the beliefs and assumptions that most teachers hold about why learners demonstrate varying degrees of involvement in classroom activities and what factors could account for this variation. This exploratory study investigated how six pre-service teachers in an initial pedagogy course in a Canadian university perceived L2 motivation and how they interpreted L2 learners' participation/non-participation. The participants wrote five journal entries over the ten weeks of a practicum during which they facilitated ESL lessons for adult learners. The first journal entry acted as a narrative since it required the participants to reflect on their previous L2 learning experiences. The other writing prompts were designed to elicit their interpretation of L2 motivation. Additional data were collected through interviews and stimulated recall sessions during which the participants watched video-recordings of their ESL lessons and reflected on their students’ participation/non-participation, as well as on classroom events and task types that might affect the learners' willingness to participate. Lastly, during a group meeting, the participants discussed topics and stimulus materials relevant to the notion of motivation. The findings that emerged from the data suggest that the multi-faceted and complex construct of L2 motivation was mainly ambiguous and under-recognized by the participants. This calls for raising critical awareness of such sensitive notions through teacher education programs.