I agree with MRL. Make sure the training sessions are positive and super fun for the dog. At this age I would also stay away from compulsion (I don't want to start a debate on training methods). Mainly, at that age you are still teaching the dog basic commands. You can't expect him to comply or worse punish him if he doesn't understnad what is being requested. Furthermore, dogs don't understand, they react, therefore its through repetition of a fun, positive act/treat they learn the action appropriate to the command. Of course results can be obtained in multiple ways, but I like to think of my dog obaying because he wants to, not because he has to.