National and state standards in the US have emphasized the importance of solving and posing word problems in students' mathematics learning for decades. Therefore, it is essential for prospective teachers (PTs) to have the mathematical knowledge necessary to teach these skills to their future students. Unfortunately, little research has investigated how PTs develop problem-posing skills. By employing thematic qualitative text analysis, the researchers identified nine distinct patterns in errors identified in K-8 PTs' posing of two-step addition and subtraction word problems, in the context of a collegiate teacher education course. These results were used to inform the initial design of an interventional task to bring awareness of common errors to PTs. [For the complete proceedings, see ED630060.]