In many scientific contexts, students need to be able to use mathematical knowledge in order to engage in scientific reasoning and problem-solving, and their understanding of scientific concepts relies heavily on their ability to understand and use mathematics in often new or unfamiliar contexts. Not only do science students need high levels of numeracy, they may be at risk of limited success in many areas of science if they do not (Lenton & Stevens, 2001). Proportional Reasoning, which is an essential element of numeracy, is critical for scientific thinking. The mathematics education literature abounds with research about the difficulties with proportionality experienced by students of all ages and yet, despite their central importance to scientific understanding, research on the teaching and learning of proportional reasoning concepts in science contexts is somewhat limited (NRC, 2012; Taylor & Jones, 2013) and generally restricted to understanding concepts such as speed, power, movement, and pressure in physics (Akatugba & Wallace, 2009). This paper addresses the lack of an explicit focus on proportionality in the science curriculum. It describes a curriculum audit that was conducted to identify science concepts that rely on elements of proportional reasoning for understanding in order to devise a science scope and sequence document to support teachers. Included are illustrative examples from this document. While this audit focused on the science curriculum to Year 10, it also has implications for senior secondary subjects.