Adolescents often do not consider sustainability in their consumption behaviours. Sustainability issues are challenging to communicate through course content alone. Against this background, the concept of fashion libraries (FLs) was introduced to adolescents at a non-denominational school in a small German city. The purpose was to explore whether the students' attitudes would change over time in response to distinct interventions and project-based learning, such as the foundation of an FL, upcycling workshops and lectures on sustainability. The sample comprised 10 female adolescents in the age between 13 and 16 years, who volunteered to participate in the clothing library project. An exploratory mixed-methods approach, including a questionnaire, two interventions and pre-and post-intervention in-depth interviews, was utilized. The findings hint at an incremental change in the students' attitudes towards an appreciation of garments and a change in behaviour. They started to reflect their behaviour and consequently reduced the frequency and quantity of their clothing purchases. To the best of the authors' knowledge, this is the first article in which an FL was founded to investigate the consumption behaviour of adolescents.