Abstract
In effectiveness literature, voices are rising to embrace learning contents beyond mathematics, science, and language. Meanwhile, international policy documents such as the United Nations 2019 Climate Action Summit Report point at the importance of action for sustainable development for establishing acceptable life conditions for current and future generations. Therefore, a candidate learning outcome for broadening effectiveness research's scope is action competence in sustainable development (ACiSD), which consists of the relevant knowledge, willingness, capacity expectations, and outcome expectancy regarding actions for sustainable development. In order to initiate adding ACiSD as a learning outcome to effectiveness research, the current study contributed to establishing that formal education plays a part in changes in students' ACiSD. Firstly, we studied how much variance in ACiSD can be attributed to what happens in classrooms. Secondly, we looked into how class groups' and early adolescent students' ACiSD changed after one school year. Following recommendations for rigour in effectiveness research, we performed multilevel analyses on survey data (question one: n = 1398; question two: n = 633). Our evidence showed that 11% of variance in ACiSD was attributable to what happens in classrooms with explained variance in the subconstructs ranging between 7.2 and 14.2%. Furthermore, individual students as well as class groups showed higher ACiSD scores when comparing measurements at beginning and end of one school year. We conclude that the classroom level matters to changes in ACiSD within early adolescents. Further research can now look into how and to which extent teachers' educational approaches affect these changes.