Research indicates that STEM-integrated curricula and pedagogies have the potential to support student learning, nurture interest in STEM disciplines, and prepare students for future careers (Apedoe et al. 2008). Through engagement in these fields, students can develop the ability to think critically, solve intricate problems, and drive advancement that maintains a steady progression of society (Apedoe et al. 2008). One such instructional pedagogy that works well with STEM integration is problem-based learning (PBL). Problem-based learning is a student-centered instructional approach that emphasizes practical experience in supporting learning (Hmelo-Silver 2004). This article describes an activity where students use the five steps of the engineering design process--Ask, Imagine, Plan, Create, improve--to solve a STEM problem-based challenge. The problem scenario in the PBL activity described here engaged fifth-grade students in a six-week challenge to design a filtration system. In this PBL activity, students learned about various states and characteristics of matter, including filtration. This allowed the students to tap into their understanding of the disciplinary core ideas related to structure and properties of matter.