The Activity Book contains both the instructor pages (first half) and the Student Pages (perforated second half). The Activity Book tells you how to use the Student Pages and has a lot of instructor support, student assignments, and teaching recommendations.
Well-Trained Mind Press' copyright allows you to reproduce the Student Pages as you wish for use within your own household. If you have more than one student, or if you prefer to keep your Activity Book intact, purchase a separate set of Student Pages (physical or digital format).
Some parents/instructors are comfortable teaching from a laptop or tablet, so they purchase the Activity Book in PDF format and print the Student Pages as they go along.
Those who teach groups of students online or in person may purchase a license to reproduce the Student Pages and other supplemental materials in The Story of the World family.
Here is more information about The Story of the World series.