In 2018, a research project funded by New Zealand's Teaching and Learning Research Initiative (TLRI) explored the impact of online citizen science (OCS) projects on the science education of primary school children in New Zealand. This article provides an in-depth case study from this project in order to share ways in which one teacher used OCS projects specifically to develop students' science capability, "Critique evidence". Comparing data from students' conversations and work with the progress indicators for the science capabilities released by the Ministry of Education in 2019 suggests that many of the students were achieving at or above the expected level. We suggest that teacher professional learning and development in relation to the intent of science in "The New Zealand Curriculum," and the purpose of the science capabilities, was a significant enabler. [Written with assistance from Markus Luczak-Roesch, Cathal Doyle, Cameron Pierson, Yevgeniya Li, Brigitte Glasson, Carol Brieseman, Matt Boucher, and Dianne Christenson.]