Schedule of Reinforcement- Weaning from treats.

I'm reading a book right now written by Patricia B.McConnell called Family Friendly Dog Training -A six week program for you and your dog.
We are just working on week 2 with Reese and are already being encouraged to begin a random schedule of rewarding, which to my surprise is working really well.
I really like to keep the dog guessing where and when the reinforcement (treats, toys, praise or quick game of tug) will be coming from. But am really surprised to find that you can start randomizing the schedule of reinforcemtne this early with some things like the sit and recall in a 12 week old pup.