Engineering design, an integral part of engineering education, is a challenging process to describe, teach, and assess. In this chapter, we describe the way we explored design process assessment in the K-12 setting. An instrument that was previously used to assess college students and professional engineers was adapted for elementary students. The students were asked to critique an engineering design process. Their responses were coded for occurrences of design process concepts. We validated the results by comparing the frequency of the occurrences of the responses in the instruction group and the comparison group of students before and after the school year. A version was created for elementary teachers and validated through comparing performances before and after a week-long engineering workshop. While there are areas for continual development and improvement, this method of evaluating design process knowledge has the potential to provide formative assessment of design learning.