Primate sanctuaries provide a solution for the increasing number of primates being taken from their home countries to support the demands of the illegal pet trade. To help end the primate trade and raise awareness about the risks this trade poses to delicate ecosystems, sanctuaries are increasingly developing conservation education programs. Education and raising awareness must be one of the primary roles of primate sanctuaries. However, there are few evaluations of the impacts of conservation education programs for school children published in scientific literature. To address this gap, we conducted an evaluation of educator-led visits of school children at Fundació Mona, a primate sanctuary located in Catalunya, Spain. Questionnaires for an experimental and control group were conducted with 3,205 school children, ages 8 to 18 from 83 different schools, to evaluate changes in their attitudes and knowledge of primate welfare and conservation. We found that Fundació Mona’s program of environmental activities had a positive impact on children, both female and male students, in terms of attitudes and knowledge of primate welfare and conservation. Although female students gave better responses regarding welfare and conservation, all children showed gains in pro-conservation responses. This study demonstrates that environmental education activities focused on children can help shape a change in knowledge and attitudes toward primate welfare and conservation. Educator-led visits of school children to primate sanctuaries such as Fundació Mona can also serve to amplify biodiversity conservation messages among children and their families. We encourage primate sanctuaries to promote empirical studies of attitudes and knowledge of primate welfare and conservation and to conduct systematical evaluations to strengthen their educational activities.