This resource from the Mathematics Assessment Project was found at OER Commons. https://www.oercommons.org/courses/finding-equations-of-parallel-and-perpendicular-lines/view. This lesson unit is intended to help teachers assess how well students are able to understand the relationship between the slopes of parallel and perpendicular lines and, in particular, to help identify students who find it difficult to: find, from their equations, lines that are parallel and perpendicular; and identify and use intercepts.