What we kids in the late 70's called spastics, and by association anyone who was a low achiever no matter what the reason.
Im now a responsible and mature father of two teenage girls who would not dream of mocking the mentally subnormal just for kicks, so did NOT curl up in hysterics when their school's drive towards 'spelling, punctuation and grammar' was launched under the banner of 'S.P.A.G'.
And I definitely did not laugh to the point of vomiting when my daughter brought her english exercise book home with the word 'SPAG' written in red biro by the teacher over each and every spaggish grammar or spelling mistake.