When I took an Obedience Class with Daisy, the instructor taught us this technique. We used choke chain collars, and when the choke collars were on the dogs, we put them in a "Sit, Stay" position, and walked a few feet away. The owners than said "Fido, Come!" [replace Fido with dog's name] and if they didn't come when you called them, you did a quick snap of the leash [called a "correction" when using a choke chain] and sooner or later the dog would learn to come when called. You could use treats to lure them, or as a reward when they listened, but our instructor was strictly on a praising method, with no treats. It worked for us.