Campaigns by zoos, aquariums, and other civil society organizations are an important tool for promoting social changes that benefit the environment. Here, we evaluate a global biodiversity education campaign's impact through a repeated-measures survey of nearly 5000 visitors to 20 zoos and aquariums located in 14 countries. By comparing visitors’ pre- and post-visit responses combined across respondents, we found significant aggregate improvements in their biodiversity understanding and their knowledge of actions to help protect biodiversity. Respondents who reported seeing the education