This study reviews the criteria for assessing reflective thinking, and investigates how the process of reflective thinking develops in preservice teachers. Reflections of preservice teachers are assessed from two perspectives: content and depth. The findings include variations in the content, and that the pace at which reflective thinking deepens depends on personal background, field experience contexts, and the mode of communication. The study includes insights into how to measure the quality of reflective thinking and how to enhance reflective thinking and cultivate reflective practitioners, including the kinds of experiences that could be incorporated in a teacher education program.