ive been teaching my pups retrieve since they were 9 wk old, there 16 wk old now and still do it... about 3-5 retrieves a day is what i do, keeps them interested.
what i do is sit infront of there kennel as they always run back to that, so they get used to running back to me, i can now do it in open fields and they come straight back.
get an old sock, tie some string to it, swing it about to get them interested, release it, as soon as they pick it up call them back.
dont be surprised if they run about all over first few tries, this is fun for them, but keep calling and they will ev