A unit study is also commonly called a "theme," a "thematic unit" or "integrated studies." With unit studies, a topic, or theme, is studied as a whole, rather than broken down into various "subjects." For example, when completing a unit study on horses, one might study the anatomy of horses (science), look at horses in art (art), figure units of measure involving horses (math), read books on horses or biographies of authors who wrote about horses (language arts), learn how horses have provided transportation for man throughout history (social studies), and so on.
Unit studies work particularly well for families with children of varying ages because each child studies the same subject, but on his or her level. For example, a preschooler might color a picture of a horse, while an elementary-aged child labels the anatomy of a horse and a high school-aged student writes a report on the usefulness of horses throughout history.