This reflective action research documents the mutual learning experiences of three education stakeholders as they construct their language assessment literacy (LAL). A?teacher educator, an inservice teacher, and a preservice teacher were the three stakeholders who took part in a project on language assessment development for ESOL students at a public school in the United States. In this project, with the help of inservice ESOL teachers, preservice ESOL teachers designed and implemented listening and writing assessments for local middle school ESOL students. During and after the project, one of the participating inservice teachers, one preservice teacher, and the teacher educator voluntarily participated in extended reflective practices via email communications, on-site visits, and pre- and post-project discussions. All stakeholders perceived the collaboration as a mutual learning experience to enhance their LAL while sharing their respective expertise.