The paper explores and describes the kinds of learning attained by a group of Hong Kong preservice teachers who worked collaboratively to develop online grammar teaching resources for school teachers worldwide. Based on the quantitative and qualitative data collected during the ongoing collaboration, lesson tryouts, and post-project evaluation, the project results reflect the value of experiential learning in preservice teacher education. The themes that detail the student teachers' experiences include textbook evaluation, professional knowledge, core competencies of teachers, and understanding of English language teaching outside the Hong Kong context.