There is also the e-marshmallow test (link is not very relevant), in which children have to face the tough choice between surfing an open connected computer with games, internet etc... and waiting patiently for the experimenter to get back. Upon the experimenter's arrival, they get a pile of marshmallows. I presume it also correlates with interesting things, though haven't found much on it.

What about kids who value internet more than marshmallows? A better test would be to promise them more time if they waited.