This study investigates the development of species knowledge among 7-12-year-old children who parti-cipated in a holiday activity, a beach school, at a marine public aquarium. The question “What could live in the environment in the picture even though you can’t see it?” was asked as a pre-test, post-test, and delayed post-test. We developed a method to assess the taxonomic quality of the answers. Animals were mentioned far more frequently than algae and plants. The most common answers were crab and fish. The activity increased both the quantity and taxonomic quality of children’s species knowledge significantly. No differences were found between two- and three-day beach schools. The post-test showed that the children perceived the affordances that the aquariums and the beach environment offer. While beach schools can serve as a small step toward ocean literacy, additional efforts from both semiformal science institutions and schools are needed to reach more children.