The responsibility lies with the candidates/campaigners to promote their own party and 'educate' their own policies as opposed to what Brexit became i.e. a slanging match and just a lot of lies bandied about each other's party - bordering on offensive, abusive, insulting etc etc. The media have a big part of the blame there though - they became volatile and created an environment to be just that.
I agree about the schooling - I don't remember ever getting taught about importance of my vote and what I could be voting for at the time. Unless you're gonna do a politics course at A-Level/Uni then I doubt you'll know complex intricacies of government and the way policies effect society and the country (or learnt it outside of school).
Not sure I agree too much about the aptitude test - I think you'd end up eliminate a lot of voters even though they'll be living in a place where some policies really have an effect i.e. high population of students in an area may want to know what their life will be like in terms of fees for uni - if they fail the aptitude test, how can they have a vote on their future? That's just one loose example though.