Citizen science is a valuable tool in environmental and formal education in creating scientific knowledge for the researchers and facilitating learning and fostering a positive relationship toward the environment and study species. We present a case study on the Helsinki Urban Rat Project in which students surveyed rat occurrence in their own near environments. According to our results, experientiality, involvement, meaningfulness, freedom to choose, ease of participation, and the rats themselves contributed to students' increased interest in participation. Furthermore, students described diverse factual, conceptual, procedural, and metacognitive knowledge that they acquired during their participation. In general, students described negative attitudes toward rats, but they less negative views on rats after participation. We reflect on the success of the citizen science project and implications of planning a future citizen science project and incorporating citizen science in formal education.