Computer Science formal education brings together old-timers from two computer-literate cultures. The curriculum is oriented toward the academic community, whose interest is in the abstraction, solution, and proofs of algorithmic problems, whereas many students are technology users, whose main interest is the manipulation of the products of technology. Ultimately, this situation leads to a culture clash, which can be resolved by designing the didactical milieux as fertile zones of cultural encounters, that is, providing the students with the motivation and opportunities to cross their cultural boundaries toward the target culture. This approach is demonstrated by describing a course in concurrent and distributed computation designed for high-school students, focusing on one lab assignment. A qualitative analysis of the processes that two students underwent as they coped with the assignment illustrates the influence of their cultural background as technology users and portrays the mutual interplay of the cultural and cognitive aspects of learning. The analysis of the performance of two classes of students reinforces the argument regarding the effectiveness of the milieu. (Contains 1 table and 3 figures.)