It all depends on the confidence of the child, if they are timid, which my ds was, it took him 1 year he is now 4, but really there arn't many children that start before then unless they are water babies!
Each child is different, I have some children age 6 in my classes that don't swim, but its generally because they have confidence issues, and havent swam much.
Children will swim when THEY are ready.
As for the same old lessons time after time, there is a teaching plan that has to be used, but should be varied so the children don't get fed up, but I'm afraid until they achieve those goals, you just have to stick with it.
Try different instructors if child not getting anywhere. Some children react differently to different teachings.
As an instructor, I'd be worried if I did not see any progression at all, within an 8 week course.
Other than that, take children play swimming to gain confidence, take arm bands off, try woggles and floats, obviously in water depth that they can regain standing.
Good luck.