I don't know how to answer that. Making changes in one's teaching is a slow and gradual process, with many dimensions and components. Some milestones for me were, more or less in that order: switching to a collaborative learning model; the gradual introduction of many learning tools (manipulatives and technology); lagging homework and assessments. Each step along that path helped me reach a broader range of kids. But I am not able to put dates on any of it.