How can Intelligent Design be taught in science class if it isn't scientific?

To be scientific, you must have a decent description of what and how something happens. For example evolution is scientific because it describes how species change over time through mutation, natural selection and genetic drift. There are literally books upon books specifically written describing only the process. Now Intelligent Design people say it is also a science. But they only "know" what happened (i.e. god made the eye) but not how it happened (i.e. god has a factory in china?). Anyone notices that?