Research findings on beliefs in second language acquisition (SLA) suggest that beliefs can have a great impact on language learners’ approach to learning, the manner in which they complete language learning tasks, and their ability to complete those tasks and achieve their goals (Griffiths &Soruç 2020). This study explores secondary students’ beliefs about English L2 speaking fluency, their own performance on argumentative dialogues, and possible changes in these beliefs over an eight-month period. Speaking fluency is a multifaceted construct and it is a widely used term in both everyday and research contexts (Tavakoli& Wright 2020). These factors might result in the coexistence of multiple conceptualisations of fluency in a given context. This study argues that this coexistence might also entail inconsistent and even contradictory beliefs about speaking fluency and the components that need to be developed to achieve it. Moreover, these beliefs might change over time. The participants were twelve secondary students in an English bilingual programme (16-year-olds: 11 females and 1 male) who audio-recorded their English L2 argumentative dialogues throughout a school year (10-13 discussions over the eight months). They completed reflective journals in Hungarian, in which they answered questions on how they felt during the dialogues, what areas they felt good and bad at, and what and how they wanted to develop in the future. In addition, they completed a qualitative questionnaire at the beginning and end of the research which focused on their conceptualisation of speaking fluency, the factors they considered important, and their language learning habits and background. The findings showed that the participants had diverse and sometimes contradictory beliefs about speaking fluency and the components that are important to develop, and that these beliefs also changed over time for some participants. / Keywords: beliefs about speaking fluency, introspective methods, reflective journals, experience sampling