The traditional high school science course sequence in the United States has followed a Biology-Chemistry-Physics (B-C-P) progression for over a century. This sequence took root in the late 19th and early 20th centuries when education shifted gears from classical studies to include a more scientific perspective to meet the demands of an industrializing nation. The initial rationale for starting with biology was its perceived accessibility—biological concepts were seen as more relatable to students’ everyday experiences. They required less mathematical rigor than physics or chemistry.

The B-C-P sequence became the cornerstone of American science education due to its practicality and alignment with the developmental stages of secondary education students. It mirrored the increasing complexity and abstraction of scientific disciplines while assuming a parallel development in students’ mathematical skills. Biology’s concrete and observable nature made it an ideal starting point for ninth graders, while the more mathematically demanding subjects of chemistry and physics were reserved for the later years of high school as students matured academically.

The longevity of the B-C-P sequence is a testament to its utility and adaptability. It served generations of students, providing a broad overview of scientific principles and methods. The sequence benefited from a straightforward structure that educators and administrators could quickly implement and manage within the constraints of school schedules and resources.

However, the traditional sequence hasn’t been without its critics and challenges. One limitation was its compartmentalization of scientific disciplines, often leading to fragmented learning experiences. Students would tackle biology without the foundational chemical principles that underpin biological processes or explore chemical reactions without understanding the physical laws governing these reactions. This siloed approach to teaching science was increasingly at odds with the real-world integration of scientific knowledge, where the boundaries between biology, chemistry, and physics are porous and interconnected.

Furthermore, as scientific knowledge rapidly expanded and technology advanced in the 20th century, science education needed to go beyond facts. It now had to develop students' critical thinking, problem-solving, and deeper understanding of the scientific process.