This chapter presents a metaphor for designing educational computing systems (ECSs) that progressively transfer to the learner an increasing amount of control in the problem solving process. The continuous variation of learner's control is segmented in a few levels. The transition from some level i to the next higher level i+1 results from the internalization of the concepts necessary to control the activities at level i. The use of reflection tools is proposed for supporting the internalization process. These reflection tools reify the control features of the learner's activities, i.e. they make concrete some abstract features of her behaviour. The next level is reached when the learner is able to use aspects refied at level i to interact with the system at level i+1. A same control concept is hence used firstly as a description language (by the system) at some level i and then as a command language (by the learner) at the level i+1. This language shift mechanism elevates the learner's level of control and her level of abstraction. It is described by analogy with an elevator that would move inside a pyramid. A floor of the pyramid corresponds to some control level. We use a formal notation to look inside the language shift mechanism and relate it to various psychological theories and current ECSs.