Yeah, that's kind of where I'm going. He's certainly intelligent, but guileless, ineloquent, and generally unwilling to apply himself to subjects that don't interest him. 

A possible slice of life side plot: the rangers have arranged an after school club of some kind as an excuse to gather without drawing suspicion, but Blue is in danger of losing his extracurricular privileges at school because of his English grade. 

Joining the rangers would definitely give him a drive he was lacking, but it also ends up taking a lot of time and energy, leaving less for school work.