Mobile devices are changing the way people work and communicate. Most of the innovative devices offer the opportunity to integrate augmented reality in mobile applications, permitting the combination of the real world with virtual information. This feature can be particularly useful to enhance informal and formal didactic actions based on student collaboration. This paper describes a "collaborative campus," originated in the physical architectural space, but exposing learning contents and social information structured as augmented virtual areas. ACCampus, a mobile augmented reality system, supporting the sharing of contextualized information is proposed. This system combines the world perceived by the phone camera with information concerning student location and community, enabling users to share multimedia information in location-based content areas. User localization is initially detected through QR codes. The successive positions of the user are determined using the mobile device sensors. Each augmented area is univocally spatially associated to a representative real wall area. Selective content sharing and collaboration are supported, enabling a user to distribute his/her augmented contents to specific users or groups. An evaluation of the proposed environment is also conducted, which considers that learning in collaborative environments is related to perceived member contribution, enjoinment, motivation, and student participation. (Contains 6 figures and 4 tables.)