Our DD hates drills but enjoys math; nonetheless learning math facts was kind of a drag. Two essentially free and easy math fact games we learned about from her first wonderful teacher were math War and math dice. In each you play two at once (cards or dice) and perform a math operation on the resulting numbers; you can keep score for the highest cumulative result or same but deduct a point if a player miscalculates. Operation can be specified or not. Much more enjoyable for DD than worksheets or flash cards.