Many education initiatives in science and technology education aim to create enthusiasm among young people to pursue a career in Science, Technology, Engineering, and Mathematics (STEM). Research suggests that personal interaction between secondary school students and scientists could be a success factor, but there is a need for more in-depth research on the actual effects of science education initiatives. This paper describes an in-depth, qualitative assessment of a technology design activity, using as a theoretical framework the expectancy-value model of academic choice Eccles and Wigfield ("Annu Rev Psychol" 53:109-132, 2002). A core element in the studied education initiative is the interaction between secondary school students and scientists. Semi-structured interviews were conducted with participating students and analysed qualitatively to disentangle the factors in their motivation to participate in this initiative and their experiences and memories gathered during participation. Last, this paper reflects on the use of the expectancy-value model for in-depth assessments of science education initiatives. Results show that interest-enjoyment values and attainment values are most important in the students' motivation to participate in the studied activity. These values are connected to educational principles of authentic practice, and of providing meaningful contexts for scientific concepts. Furthermore, results show that the interaction between students and scientists is not automatically a success factor. Disappointment in this interaction, can cast a shadow on students' whole experience. This leads us to propose to include an additional factor in the expectancy-value model of achievement related choice: educational environment, including "personal interaction" as an element. Adding this factor would--in our opinion--create an even better framework for in-depth assessment of science education initiatives.