Existing spelling assessment tools were not designed to meet the needs of primary preservice teachers learning how to teach spelling. In this action research, I developed a tool to guide planning for spelling instruction for preservice teachers who found it difficult to identify appropriate teaching foci for children's spelling errors. The tool has three sections: an error analysis grid; a guide for planning specific foci based on error analyses; and, a checklist to review the process. Perceived strengths of the tool are making obvious the key features in the development of spelling knowledge with an emphasis on phonology and morphology and including guidelines for planning differentiated spelling instruction.