If anyone is old enough (50+) to have seen the original Lassie series, but had trouble remembering Tom Rettig, they are showing the shows on PAX 51 M-F at 5:30 pm Eastern on the Sky Angel satellite service.
As soon as I saw one show, I immediately remembered Tom playing Jeff Miller. I would guess that he played Jeff Miller as long or longer than Jon Provost played Timmy.
And he was an exeptional actor. I am glad I had my memory refreshed.