This study aims to develop an acquisition-oriented STEM activity that primary school teachers can implement in the classroom. The design-based teaching activity developed and implemented within this study is intended to be presented as an example of an activity suitable for STEM education focused on mathematics lessons. The activity was developed in line with the design process indicators within the K12 engineering education framework. The steps of this learning model are (1) problem and background, (2) plan and implementation, and (3) testing and evaluation. The activity particularly targets elementary school students produce an engineering design product using simple and low-cost materials. The fourcriteria presented to the students in this process were (1) apartments receiving light, (2) being earthquake resistant, (3) being economical and (4) aesthetics and marketing. Throughout the design process, the criterion that students had the most difficulty was observed as the sun exposure of the flats. Also, most of the students focused more on the aesthetic criterion than other criteria, and they emphasized this criterion most in the marketing process of their products.