A lack of qualitative studies examining adolescent students’ voices regarding the contextual, relational, and self-regulatory factors that drive their language achievement has been observed. Therefore, the present study aimed to address this issue. Sixteen face-to-face semi-structured interviews were conducted with secondary school students in Greece to document and analyse their perceptions of the factors that influence language achievement. The study was guided by social-cognitive theory and models of self-regulated learning. Computer-assisted thematic analysis was performed using abductive open coding followed by refinement of codes. Three overarching global themes were identified in line with theoretical expectations, namely personal factors (motivation and self-regulatory strategies), relational factors (teachers’ practices, parental achievement expectations, peer influences), and structural factors (the educational system). Afterwards, an abductive thematic network analysis was conducted to explore and theorise about potential relationships between the emergent themes in the data. It was found that parental expectations for higher performance and the teachers’ behaviours were associated with students’ language achievement. Task-related characteristics and peers influenced students’ regulation of effort in learning. The students believed that they were not objectively graded and frequent summative assessments created test anxiety. The findings are discussed in light of existing empirical evidence and in terms of educational implications.