When our kids were in elementary school my husband (a math and history teacher) would play a game called 'Candy Store' to help them with their basic math skills. It's simple, fun and you get a very kid friendly reward!
The game starts with whatever set up you desire depending on the energy you have to put into it. My husband would sit at the kitchen table with one of our kids and have a pile of candy in the center of the table, whatever their favorites were at the time.
He would be the 'store manager' and payment would be given in cheerios!
Our child would have a zip lock bag full of cheerios and then my husband would say;
"So you want to buy some Candy? Well this red candy cost 5" and they would count out five cheerios...then he would announce;
"Oh wait! That red candy has bugs in it! Ewww.. may I interest you in the green one? That will be 3 cheerios".
Then our child would have to take their first 5 and subtract to get 3.
He would play this with silly reasons for why each candy couldn't be bought...add or subtract for a new one, then after ten minutes (not much longer for that age or they lose interest and it's no longer a 'game') he would let them pick one candy from any in the pile.
We would explain exactly how the game worked ahead of time so they would understand that they would be getting a candy at the end but it would be only one candy.
Each day after school the kids would ask;
"Daddy! Is the Candy Store open?? Can we Play?"