Drawing on theories from developmental psychology (i.e., implicit theories; Dweck & Leggett, 1988) and organisational psychology (i.e., Psychological Capital; Luthans, Avolio, Avey, & Norman, 2007), the current study explored the dimensionality and malleability of mental toughness among 230 female adolescent netballers aged 11 to 17 years (M = 14.98, SD = 1.51). The analyses support a relationship between the six core attributes of mental toughness, but less support for the existence of a core mental toughness factor. Contrary to expectations, two implicit theory clusters emerged: A high growth/low fixed group, and a moderate growth/moderate fixed group. When compared with the moderate cluster, the high growth/low fixed group reported significantly higher levels of the mental toughness attributes, with the exception of buoyancy. Although requiring replication and extension, the results of the current study provide support for the dimensionality and malleability of mental toughness in adolescent performer populations from other well-researched perspectives that have remained largely unexplored in sport.