What is the difference between a past and a present participial phrase?  And what is a gerund?  Now I can answer these questions confidently.  What made me learn it was that the book keeps things simple—you learn clear rules without a lot of exceptions.  I think the most important part was the mastery exams.  This is where you have to know certain material (like memory sentences) before taking the test.  I did get some zeros, but now I really know the material.