This study explores the influence of self-assessment of vocabulary competence on a group of students' oral fluency. Twenty-four young adult learners participated in a learning process that promoted their oral skills and vocabulary development. Self-assessment was mainly examined through the analysis of students' learning logs, field notes and artefacts in the form of audio recordings. By contrasting and analysing data sources, and the results obtained from pre- and post-speaking tasks, through a mixed method design approach, it was found that when students self-assess, they are able to acknowledge their learning strengths and drawbacks. This practice enabled students to set learning commitments, use learning strategies that also allow them to raise awareness and take further actions, while self-monitoring them. Consequently, initial improvements in students' oral fluency development were evinced through the implementation of a systematic cycle that applies self-assessment as a formative assessment source. Thus, the students entered a process in which they gradually become more able to self-monitor, judge and react towards their own gains in language and learning. Findings highlighted the value of goal setting as an essential component in self-assessment. Further longitudinal studies may well support the long-lasting effects of this strategy in similar educational contexts.