My school offered an ASL elective for a few years using http://www.asl.tc, a website that has a rough curriculum. It costs about $60 per year for a student account, but it offers lessons, quizzes, and tests.
Pros: All of the material is accessible online, there is a built-in gradebook that contains all of a student’s records, the material is clearly divided with a school setting in mind, supposedly you can get a certificate of completion, a teacher doesn’t really need to know ASL.
Cons: Most of the materials are what the owner of the website uses in his classes (he teaches ASL at a college level), so they sometimes make little sense out of context. it costs money, every once in a while the website mysteriously goes down, students get no experience actually making the signs themselves..
We supplemented it with requiring students to write dialogues using new vocabulary which they then demonstrated to a teacher. Second year students were required to research the signs necessary to demonstrate the weekly Bible memory passage.