The goal of this article is to understand how the pro-environmental behaviour (PEB) of secondary school students can be encouraged. In an exploratory study, we examine to what extent pro-environmental cues--that is, 'situational strength' (Mischel, Psychological Review, 80(4):252, 1973)--were present in schools and whether students in 'stronger' situations reported higher levels of PEB than students in 'weaker' ones. Moreover, we examined relationships between student characteristics--gender, perceived behavioural control (PBC), pro-environmental attitudes (PEA) and intentions (Fishbein & Ajzen, "Belief, attitudes, intention, and behavior. An introduction to theory and research." Reading, MA: Addison-Wesley, 1975)--and their PEB. A sequential mixed method was used, utilizing data from three Dutch secondary schools. Survey data covering 179 students showed relationships among students' gender, PEA and intentions, and PEB. Qualitative data--derived from semi-structured interviews with staff members, structured assignments for students and observations--showed differences in situational strength between the schools. Moreover, the data suggest an interplay between student characteristics and situational strength in affecting PEB.