One of the best ways of explaining something to an autistic person is to use Social Stories (TM). You might try it both for explaining turning in homework to your grandson and reminding him to turn it in, as well as maybe to explain autism to your husband.

Social Stories?

I have been to one of Carol Gray's trainings. Writing these stories isn't that hard, but you do have to learn the guidelines and follow them. There are a few important things to know, like not making the child feel picked on by being critical or making fun of him, even unintentionally, in the story. It is a way to use a story to describe a situation and responses in a non-critical way. Maybe the teacher or the school would invest in some training or a book, or you can also find the books in the library or get them from the website.