The concentric circles approach to organizing content involves introducing a subject matter over multiple years, with elementary knowledge provided in introductory years and more advanced knowledge added each subsequent year. A topic is broken into sub-topics that are allotted to different classes based on difficulty. This allows steady, gradual coverage of a topic from basic to full knowledge. It is considered a psychologically sound approach that maintains student interest through revision and presentation of small portions over time to create lasting impressions. Teachers must take care that topics are neither too long nor too short each year.