As part of a multiyear research project investigating the affordances of online citizen science (OCS) projects for enhancing school students' learning in relation to science and digital technology, teacher-researchers have designed and implemented classroom interventions incorporating one or more OCS projects. The project is situated in New Zealand, and each intervention has embedded an OCS project within a wider unit of learning focusing on one or more "science capabilities" (Ministry of Education, n.d.). This article presents one of the case studies generated in the wider project. It is of a Year 9 class that engaged with the OCS project Planet Four as part of a wider inquiry unit emphasising the science capability Use evidence: "Can humans live on Mars?" The findings demonstrate that a deliberate focus on using evidence throughout the unit gave students multiple opportunities to practise and develop this science capability within the engaging context of space travel.