Jason and Marceline continues the stories of Jason Herkimer and Marceline McAllister, who appeared in Spinelli's earlier novel, Space Station Seventh Grade. Jason and Marceline begins with Jason and Marceline walking to school together for their first day in the ninth grade. It ends with them attending their ninth-grade prom.
Jason is concerned with being accepted by and liked by his friends.
Marceline is more self-contained and inner-directed; she is more concerned with doing what she feels to be right, as well as with her own personal interests. Even though these differing attitudes cause some problems in their relationship, they begin and end the book as boyfriend and girlfriend.
In the course of their year in the ninth grade, they face all kinds of pressure. Jason feels pressured by his peers into sexual experimentation.
Marceline, however, demands that the two of them go at their own pace...