When my kids were small, there was one computer game that I refused to let them play for a while, called "Dungeon Keeper". The premise of the game was that you were the "Dungeon Keeper" and your job was to keep Heroes from rescuing your prisoners!
I did not want the kids putting themselves into that mindset so refused to let them play for a while.
And the time my kids were in 5th grade, 4th grade and 3rd grade. They kept bugging me about the game, and I requested that my husband only play it after the kids were asleep. That didn't fool them. They kept asking. Eventually, though, I told them that if they would take an algebra class program and pass the test, I'd let them play. I figured that would put the date comfortably in the future.
My fifth grader, zipped through the course, and qualified for the game in about a month. My fourth grader took about 4 months. The 3rd grader didn't have the basic math to move on to algebra yet, so I had to teach her multiplication and division first, and after about a year, she qualified for the game.
So much for my strategy.
However, the game didn't seem to hurt them- and they all surpassed me in mathematics a while ago. It's easy for them, since they learned it young. So, I didn't get what I wanted, but I "won" anyway.