This case study examined the relationship of problem-based learning (PBL) and sustainability education in a combined fifth and sixth grade classroom in the northeast U.S. Research questions focused on PBL instructional strategies that promote sustainability education, skills and understandings promoted by PBL, and the extent that PBL affects students’ sustainability consciousness. One teacher and eleven students participated. Problem-posing, reconstructionist, and sociocultural theories framed the study. Relevant themes were identified in a review of sustainability consciousness (SC) and PreK-12 PBL research reports. The themes revealed that SC is a growing framework with which to assess sustainability education and PBL research has strong links with sustainability education learning outcomes. Survey, interview, artifact, and observational data were analyzed to understand the fifth and sixth grade class as a case study in sustainability education. Results include a learning environment that emphasizes a pedagogy of sustainable thinking, student exhibition of sustainability education skills and understandings, and a lack of quantitative evidence of growth in students’ SC contrasted with evidence of SC in students’ written work. Findings affirmed prior PBL research focused on group collaboration, interdependency, and reflection. The study identified the need to study PBL in real-world contexts rather than only through problem scenarios. Contributions to knowledge include adding to PBL research literature, highlighting the importance of learning experiences designed to meet a school’s mission, and increasing the use of a new survey instrument. Keywords: Sociocultural, reconstructionism, problem-based learning, wicked problems, sustainability education, scaffolding, collaboration, interdependency.