Recent discussions about student learning in the mathematics education community have increasingly focused on learning trajectories. Indeed, over the past decade, there has been a considerable increase in the number of studies and books published about learning trajectories in mathematics. For example, some researchers have developed and tested LTs (e.g., Clements, Wilson & Sarama, 2004), designed teacher professional development focused on LTs (e.g., Wilson), and still other researchers have designed diagnostic assessments of student understanding based on LTs. In this presentation, our goal is to contribute to this body of research and present a curriculum-based hypothetical LT for middle school algebra, with a particular focus on proportional and linear functions. In doing so, we report on our work as part of the iFAST project, and make visible the process by which we developed this initial hypothetical LT, highlighting the considerations, decisions, and challenges we faced as part of this work.