Mobile devices, augmented reality (AR), and outdoor games can be mobilized to promote Education for Sustainable Development and, thus, to sensitize to nature conservation. The EduCITY project combines mobile learning, AR, and environmental sensors towards sustainability education and creates opportunities for citizens to contribute to their city's sustainability. This paper presents a study that articulates the previous project, the EduPARK, with the current one, the EduCITY. While EduPARK was developed within an urban park, EduCITY expanded its geographical area to the entire city. This study aims to analyze students' perceptions regarding changes in their nature conservation attitudes after exploring an urban green park in a mobile AR game-based learning activity. For this purpose, 233 basic education students (from school-year 5 to 9) played a game for environmental education, available in the EduPARK app, at the Infante D. Pedro Park (Aveiro, Portugal). Through a mixed method approach, data collection was focused on students and included two questionnaires, applied before and after the game activity; a focus group guide; and an observation grid. Results show a strengthening of positive attitudes towards nature conservation. Moreover, students mentioned that their nature conservation future intentions are focused on preserving natural resources, combating resources' waste, recycling waste, reducing pollution, and protecting fauna and flora. Students also revealed willingness and concern to teach friends and family about what they have learned with the EduPARK game. The EduCITY intends to give continuity to these practices throughout Aveiro city. This is anchored on a community-based participatory project integrating AR location games based on challenges, to be explored in the city, in formal, non-formal, and informal educational contexts, in a socio constructivism approach. This study adds to the literature on education for Sustainable Development, by revealing that it is possible to sensitize school students to nature conservation through mobile AR game-based approaches in the outdoors, which can be a first step to promote positive nature attitudes. [For the full proceedings, see ED639391.]