Discovery learning in mathematics in the domain of probability based on hands-on experiments is normally limited because of the difficulty in providing sufficient materials and data volume in terms of repetitions of the experiments. Our cooperative, computational modelling and simulation environment engages students and teachers in composing and simulating stochastic experiments, e.g. throwing dice or drawing balls, playing lottery games. It also facilitates validation and presentation. Engaging teachers in the design process led to the complementary development and evaluation of several learning activities in German secondary schools. Evaluating the results of our action research work indicated the potential of our approach for expanding traditional mathematics instruction when assisting students to develop a sustainable conceptual basis of probability principles, offering them a higher degree of responsibility for their learning. (Contains 6 figures and 1 note.)