In Australia, many Year 10 students choose not to enrol in Year 11 and 12 intermediate and advanced mathematics courses, despite having the ability to complete these courses successfully. Girls, in particular, remain significantly underrepresented in such courses. In this study, Year 10 students identified by their teachers as capable of succeeding in an advanced Year 11 mathematics course attended one of eight focus group sessions. In these sessions, they discussed the factors they considered in choosing their Year 11 mathematics courses. The data were analysed through a combination of directed and conventional content analysis, to capture both established importance factors in mathematics course choice, and potentially new or context-specific factors that arose within this group. Intrinsic value, utility value, generalized mathematics self-efficacy and sociocultural influences were cited most frequently as important factors in students' decision-making. Findings not only affirmed the relevance of expectancy-value theory for describing the motivational factors that influence students' mathematics course choices, but also underscored the need to consider the sociocultural contexts within which these choice decisions are made.