This article explores the vertical alignment of two high school classes, biology and chemistry, around the core concept of biodiesel fuel production. High school teachers and university faculty members investigated biodiesel as it relates to societal impact through a National Science Foundation Research Experience for Teachers. Using an action research approach, two high school teachers created and implemented biodiesel lessons in both biology (biochemistry algae focus) and chemistry (transesterification focus). This article describes the extent to which this integrated STEM biodiesel lesson, which is vertically aligned in one high school, affected the students' skills and attitudes in relation to STEM subjects. The lesson plans used and the student outcomes based on the biodiesel activities are provided on the basis of a year's implementation. Overall, student skill sets and attitudes improved based on pre-posttest data and classroom indicators, such as student questions. One implication of this work includes a stronger integrated STEM vertical curriculum that could be implemented in any biology and chemistry program, especially in advanced placement (AP) classes such as AP chemistry, to encourage and engage students in discovery, inquiry-based learning, problem-based learning, engineering design, and creating experiments that have a real-world applicability such as those with socio-scientific issues. The notion that science disciplines are an interconnected web of concepts is highlighted.