We started doing it on a fairly casual basis when our son was 10 or 11 months, and even at that late age we found it (and still find it) so helpful. He was getting upset at the table, banging on it and pointing, and we realized that if he could ask for more or for water it might help his behavior. It really made a difference for us! We didn't take a course or anything, just use a book and look up words as we need them or think they would be helpful. It's really been an organic process for us ... when it seems like he's trying to communicate something that we don't have the word for, we look it up and start using it. He learns fast, and generally it just takes a few days for him to get it. Right now (he's 17 mo) he knows and uses more, milk, water, cracker, sea cracker (our word for nori, his favorite snack) bed, dog, poop, wash hands, hungry, and book. It's funny, some of these words he speaks and signs at the same time, some he only signs, and there are words that he speaks but doesn't sign. As I said before, we're pretty casual about it, but I think anything that helps our kiddos to communicate is good, and it's been great for us!