Just taking a class will not do the job, though it might serve to spark the learning process. Like with all things, you have to teach yourself. And you must learn from the plants themselves, spending time with them, looking at them under the microscope, and coming to grips with what other people have written about grasses in the books.
Field Guide to Grasses of California by James P. Smith Jr. Although I live in Arizona, I have found this guide invaluable. The author has a friendly style and explains things that others tend to leave unexplained. For example he will tell you that their is an ongoing struggle to place all the species into one genus by one group and to place each in its own by another. The photographs are excellent and helpful.
A Field Guide to the Grasses of New Mexico, 3rd edition by Kelly W. Allred. This is a nice book with good line drawings. A bit hard to get, but worth the bother and the next best thing to an actual book on the grasses of Arizona.
Agnes Chase's First Book of Grasses. This is intended to be a set of first lessons for beginners, but I find it just a bit tricky, yet it is providing me with a path to learn the grasses.
How to Identify Grasses and Grasslike Plants by H. D. Harrington This is an excellent and useful book. Harrington has a way of teaching things and aims to be helpful. The glossary in the back of the book is invaluable and works well alongside the book by Agnes Chase.
Manual of the Grasses of the United States by A. S. Hitchcock. This was "the book" for many years. Mine is the second edition, dates 1950. It allows me, with a known grass in hand, to read a description and try to find the features on what I have in front of me.
Also of potential use is the section on the Poaceae in the Jepson Manual (page 1405). It affords terse descriptions and sometimes useful drawings.
Tom's Plant pages / email@example.com