The development of mobile devices, such as smartphones and tablets, has led to a new kind of learning environments: ubiquitous learning environments. These environments are particularly interesting in the framework of school learning in museum, as they permit to provide learning content to students, adapted to their positions and interests. The students are free to move in the museum and the ubiquitous learning environment provides authentic learning situations. These environments are thus an alternative to classics guided tours which limit drastically the freedom of visit (for instance, during a guided tour, it is not possible to contemplate an artwork as long as you want). We present in this paper the design of an ubiquitous learning environment named CALM (ContextuAlized Learning in Mobility), for school learning during museum visits. In CALM as well as in other ubiquitous environment, the main challenge is to reconcile the freedom of movement and action, that characterizes authentic situations, with pedagogical control by the teacher, necessarily limiting this freedom. Our system aims to provide learners with situated interactions, while giving teachers the opportunity to integrate learning objectives that will influence the proposed interactions. We use semantic proximities over a semantic model of the domain (cultural heritage) and context (e.g. position in the museum, activity) to automatically generate contextualized learning activities: artworks suggestion and comparison, serious games based on what the learner has seen. We present the use of semantic rules to enable a loosely-based control of these activities by the teacher (thematic control) together with a fine direct control of proposed activities (contextual control).