Guitar songleading is a critical component in music education and music therapy training curricula. However, at present, there is no standardized instrument to evaluate guitar songleading performance that is both valid and reliable. The purpose of this article is to describe the construction, development, and testing of a guitar songleading feedback form devised specifically for music therapy and education majors, but also applicable for other types of students. The guitar songleading performance scale (GSPS) was designed to provide specific feedback and constructive criticism for music therapy and music education majors in an efficient manner. Experts in guitar, music therapy, and music education were interviewed and provided feedback throughout the development of the GSPS to ensure its face and content validity, practicality, usefulness, and usability. Inter-observer reliability was found to be high during 105 songleading evaluations. Longitudinal data indicate that over the course of a semester and year, students' guitar songleading performance scores increased on the GSPS in accordance with their skills. This study suggests the GSPS can be a practical, useful, reliable, and valid measure of guitar songleading performance. Future research can provide additional data and explore other aspects of reliability and validity in the GSPS. (Contains 4 tables.)