A student often meets a conflict between conceptual and procedural knowledge: does (s)he need to understand for being able to do, or vice versa? Hence an important research question is how pedagogical solutions affect the relation between the two knowledge types. Our theoretical analysis and practical experience evidence that desired links can be promoted when the learner has opportunities to simultaneously activate conceptual and procedural features of the topic at hand. Such activation is considered for interactive learning that utilizes an able technological tool, the ClassPad calculator. In a sequence of examples, we will show how this tool can be exploited to develop both informal and formal mathematical knowledge.