Autism is a hugely wide-ranging spectrum. It sounds as if your grandson is somewhere on the higher-functioning scale. Persistence with educational establishments is your only way forward - difficult at the moment.
My neighbour has 2 sons, both are autistic; one is fine, shy, a bit withdrawn and cautious but pleasant and willing to interact with us. The younger is much deeper in the spectrum; cannot stand sudden noises or any changes (his screams and tantrums disturb our life and his dad escapes as often as possible) but he is fixated on numbers and I can usually get on terms by holding up fingers and asking him to add, multiply and divide.
Last year the best reader in Yr. 7 (where I helped with literacy) was autistic - I sought out poems, bits of Shakespeare for him.
School has to be the first point of call. You say they are no help. Well, it is a tough time for them so try again. If still no joy - demand to see an Ed. Psych.. It may take some time, but keep at it, please.