In this case study, basic school (8th grade) students’ (N=24) problem-solving processes are studied while implementing a design-based science learning (DBSL) approach. DBSL combines the processes of engineering design with scientific inquiry attempting to engage students in scientific reasoning through solving authentic problems. Three DBSL modules are developed by the research team within which students are expected to design an ice cream and a soda „machine“ plus a battery from simple and easily available materials. It is expected to find out: (a) how science knowledge learned before or during the inquiry session within a DBSL module is transferred to and applied in a design situation; (b) what are the characteristics of students’ scientific reasoning while solving different types of problems in DBSL setting; (c) what kinds of peer interactions can be observed during DBSL activities? Data are gathered by video recorded classroom observations and students’ written reports. Written transcripts of classroom discourse are analyzed interpretively using qualitative content analysis approach. Data analysis is expected to be finalised by May, 2016. The findings from this study have potential to improve our understanding of how students construct knowledge while solving complex problems in DBSL setting but also provide practical guidelines for teachers to facilitate further adoption of DBSL in science classroom.