This study aimed at exploring how high school students deal with designing an information system, for example, for a small business or a medical clinic, the extent to which students develop as independent learners while working on their projects, and the factors that help or hinder fostering students' design skills. The three-phase dual-loop (TPDL) model for system design is proposed, according to which design consists of "conceptual design," "structural design" and "detailed design," and includes a "human-driven" feedback loop and an "instrumentation-driven" feedback loop. It was found that the design of a real-life system is a complicated task for high school students because it requires the integration of conceptual knowledge, primarily in the phase of defining a system's objectives and planning its general structure, and procedural knowledge, for example, in the phase of handling the detailed design, implementation and testing. The common situation in schools is that students learn and practice using procedural knowledge, whereas achieving conceptual knowledge is a long-term process. Therefore, it is essential to engage students in design tasks of increasing complexity from early stages in school in order to enable them to accumulate experience and construct their own knowledge about all phases of system design. (Contains 1 table and 3 figures.)