I am currently reading a most enjoyable series where the protagonist is in seventh grade.

As a Brit I have not grasped the age of this pupil (student?)

In Britain we start school at the age of five and attend "primary one. WE stay in primary school up to primary seven when at the age of twelve we move on to secondary school. (The big school) This is where we proceed through secondary one to secondary four where we leave at sixteen. There is an option to stay on for an extra two years i.e until the age of eighteen but it is not mandatory.