Attention is increasingly being paid to integrated science, technology, engineering, and mathematics (STEM) education as a way to increase the workforce for STEM-related careers as well as to promote STEM literacy among citizens. This means that all students, including those who are educationally disadvantaged, are expected to not only acquire STEM knowledge but also to apply it to relevant situations in the future. Among the various approaches to STEM education, the design-based approach is promising. Although a significant amount of research has investigated students' STEM learning as a result of the design-based approach, little research has addressed the transfer of such learning, especially in the case of socioeconomically disadvantaged students. This mixed-methods research with an embedded design examines whether 18 ninth-grade students, who are from low-income families and attend an underfunded school, developed an understanding of torque and examines their ability to apply such understanding to new situations. Data were collected using a multiple-choice test comprising both conceptual and application questions (i.e., quantitative data) with prompts for students to write the reasons for their answers (i.e., qualitative data). Based on Wilcoxon signed-rank tests, a non-parametric statistical method, the quantitative results indicate that the students' scientific understanding significantly improved, but they struggled to apply that understanding to new situations. These quantitative results are augmented by an information-rich student and discussed based on a theory of learning transfer. Recommendations are proposed for improving the design-based activity to ensure STEM education is inclusive.