L.S.
I'd suggest trying a class first. I don't know where you live, but Kindermusik has demo classes at the public library. You might try there first since semester classes (I think) run a bit longer than the summer ones. That way you can try it before you make a commitment.
I tried the signing class when my son was about 9 or 10 months. I also tried two summer session when he was older too (about 18 months or so). I was really frustrated because my son is ACTIVE and the other kiddos were doing things like sitting in their mommies laps and holding hands and other things. My child wanted to run around the entire time. The teacher (Heidi who is really nice) was cool with that but I felt a little like the "bad parent".
Even now if we go to the library for Kindermusic, he does the same stuff a whole year later. He loves music, but I guess just doesn't like the structure of it. The other teacher doesn't take so kindly to wild children like mine. (I'm joking here because other than running around, he's not a wild man....really.) So I guess what I'm saying is.... it wasn't fun for me. My son? I think he has just as much fun elsewhere without having to pay the hefty tuition. This is not to say you and your child won't like it. I'm just saying, try it first to see if you like it before dropping all the money on tuition.