Purpose – Mobile devices used in educational settings are usually employed within a collaborative learning activity in which learning takes place in the form of social interactions between team members while performing a shared task. The authors aim to introduce MobiTOP (Mobile Tagging of Objects and People), a mobile annotation system that allows users to contribute and share geospatial multimedia annotations via mobile devices. Design/methodology/approach – Field observations and interviews were conducted. A group of trainee teachers involved in a geography field study were instructed to identify rock formations by collaborating with each other using the MobiTOP system. The trainee teachers who were in the field were guided by their lab counterparts on the tasks required to identify the rock formations. Findings – Participants were able to appreciate the fieldwork task as it augmented their classroom lessons. The system allowed them to communicate with one another in order to meet the objectives of the study. However, there were some technical difficulties in relation to the affordance of the mobile and web applications that affected the usefulness of the applications. Originality/value – This study reports the design and implementation of a mobile annotation system that was evaluated in an actual classroom setting. The results of this work have implications for both mobile applications design and mobile learning.