This study used an explanatory mixed methods research design to examine the scaffolding strategies of middle school teachers during a design problem-based learning (PBL) unit. Both quantitative and qualitative techniques were used in data collection and analysis, and the findings were integrated for interpretation. Our analysis of classroom observations revealed that teachers relied heavily on soft scaffolding throughout the five days of instruction. In addition, both classroom observations and semi-structured teacher interviews revealed that the teachers' primary goal for scaffolding was to facilitate students' cognitive structuring. Qualitative data collected through teacher interviews were used to further explore how the teachers made sense of scaffolding. Suggestions are made for incorporating distributed scaffolding in design PBL makerspaces which tend to be highly complex and place a heavy cognitive load on learners.