Personally I wouldn't do a pup class at Petsmart just because it's too distracting. I took Sanity to Petsmart just for shopping and they happened to be having a class there. All the people IN the class stopped and clamored around him. I would hate to see what happened if I was in the class and the passerbys stopped. A half hour class would take two hours! Not to mention it's rough for the distractions. You didn't mention if this was a puppy class or a puppy kindergarten. The major difference being that in class it's more intensive learning, and kindergarten it's more like "Learn to play nice".
I would ask around, see if you can get some suggestions. If all else fails, turn to the phone book. Call laces up, ask to observe a class. I lucked out at my training center. I went to work with my dad one day, (He was a sign Salesman at the time) and he was selling this place their sign. I couldn't believe how huge this place was and it was all for dogs? I started going as soon as they opened and I never left. Trust me, if you find a place like that you'll never leave, and you'll never regret it.
Ang