Mr. Jason is Callum and Sephy’s history teacher at Heathcroft. They both find him insufferable because of the way he treats Callum and the other noughts: he regularly insults them, gives them poor grades for no reason, and generally acts like he hates them. When Callum eventually confides in Mrs. Paxton about what’s going on in Mr. Jason’s classes, she insists that Mr. Jason doesn’t actually hate the noughts, because his mother is a nought. With this information, things start to fall into place for Callum (this, for instance, explains Mr. Jason’s lighter complexion). But when Callum brings Mr. Jason’s parentage up in conversation with Mr. Jason, the teacher’s reaction suggests that having a nought mother doesn’t make Mr. Jason more sympathetic—indeed, it makes him frightened and hateful of those society deems to be lesser.