I think this is called varied practice and that the idea has been around for awhile. The book Make It Stick[1] discusses a study that had 8 year olds toss beanbags at a target. For one group, the distance to the target was varied. For another, the distance to the target was fixed. At a later time, both groups were tested and the group that practiced with a variable distance performed better than the fixed distance group.

[1] http://www.amazon.com/gp/product/0674729013