Adaptability is proposed as individuals' capacity to constructively regulate psycho-behavioral functions in response to new, changing, and/or uncertain circumstances, conditions and situations. The present investigation explored the internal and external validity of an hypothesised adaptability scale. The sample comprised 2,731 high school students. In terms of internal validity, exploratory and confirmatory factor analysis (EFA and CFA) suggested a reliable higher order adaptability factor subsumed by a reliable first order cognitive-behavioural factor and a reliable first order affective factor. Multi-group CFA indicated invariance in factor structure as a function of gender, age, and language background. Further, age (younger adolescents), language background (non-English speaking), and parents' education (higher levels) predicted higher order adaptability, while gender (males) predicted first order affective adaptability. In terms of external validity, consistent with hypotheses, higher and first order adaptability was differentially associated with cognate/aligned factors (personality, implicit theories of ability, buoyancy) and also with psycho-educational wellbeing "outcome" factors (achievement, enjoyment of school, meaning and purpose, life satisfaction). Findings hold theoretical and empirical implications for researchers and practitioners seeking to better understand the constructive regulation of individuals confronted with situations involving novelty, change, and uncertainty.