Currently, I've been teaching a small group of friend's kids (3 kids plus my son) preschool and decided to try the Deluxe Teaching Kit that I received from Baby Sign Language with them. I did a test run with some signs just with my baby girl who is 10 months now, and my son who is 3 saw me and picked up on them so quickly! Now every time I say/sign milk to my baby girl, my son will come, say and sign "more milk." Then with my preschool kids, I taught them 4 words each week (1 per kid) using the flashcards and then an additional word that corresponded with that week's letter. My son knows ALL of them already (since I'm with him a lot)! The other kids are starting to pick up on them too (during our time 2x a week for 1.5 hours). I have become so excited to see how quickly they are picking them up. So far my son knows all of these signs just from the last 2 weeks: more, milk, please, thank you, sorry, car, train, boat, book, fish, rainbow, airplane, potty. He tries to do the alphabet with me too.
One night when I was putting my baby girl down for bed, he screamed for me. I come running back to where he was, and he's like "Look Mom, I can do it! See!" as he signs "Airplane" (same fingers as I Love You but pointed down) - pretty tricky sign for a 3 year old. It was so cute to know that he had been practicing all by himself!
It hasn't been hard at all to teach them either! The flashcards are so simple to use and are very durable. The dictionary too has been great for finding words that correspond with my letter of the week. I've tried other flashcards and posters before along with watching movies, but the flashcards were too small, hard to read and not durable. The posters weren't very pretty or easy to read either. Movies are hard to follow sometimes. Baby Sign Language's flashcards are 4x6 - large and durable. They're easy to read on their white background too.
Right now they even have a deal on their Deluxe Teaching Kit that I would highly recommend!