A friend of mine has a rather precocious daughter with poor impulse control, and asked if I knew any behavior games that encourage children to think out the consequences of actions before they do them.
I'm familiar with the Good Behavior Game and the like, but standard conditioning hasn't been very effective with this child in the past. She's quite clever about subverting rules when possible, and shutting down entirely when subversion fails.
Please, one suggestion per thread so that the karma thing can do its thing.
I would recommend picking a particular goal, working on that, and moving to the next only when the first is complete.
At 6-8 years of age, anticipating consequences is a pretty big step. I'd recommend working on that first, as it may make the latter more easily resolved.
She's probably too young for chess or roguelikes, as other commenters have suggested. (If she's advanced enough to play roguelikes, Dwarf Fortress would probably be better.) Checkers should be within her age range. However, I recommend eliminating the rule that you -have- to capture a piece if the move is available.
If checkers is a bit advanced, Tic-Tac-Toe is also an option.
(I don't know why this comment is sitting at -2. It seems perfectly ordinary to me.)