Students were given a practice booklet and told to practice as much or as little as they pleased. The other half took it after they practiced. The tendency to create a handicap gets stronger as boys get older. It might be a good idea if classroom teachers would bolster or affirm all students' self-evaluations before tests. That way students would try to do their best rather than create excuses.
People create a disadvantage for themselves as a way of protection.
If they don't do well, they say it was because they didn't prepare, not because they didn't have the ability. Unfortunately, putting yourself at a disadvantage by self-handicapping makes it more likely that you will fail.