Have you seen these at Barnes and Noble? I guess they have been around for a while, but we just found them a few months back while we were perusing the children's section. Brain Quest Cards are essentially trivia flashcards that are bound together in one corner (which means they won't get spilled out all over the floor, yay!). The questions are meant to be read aloud to the person/people being quizzed, and the answers to the trivia can be found on the following card.
Each set of cards comes with a recommended age. I have found cards for children as young as 2, and for as old as 7th Grade. The cards are pretty small- small enough that I can stash a few in the diaper bag or my purse when my kids and I go out. That way, we have a fun trivia game to distract us from the inevitable delays we will experience in the city....like waiting for the subway. These are also great for long subway rides, or waiting in line. Because my two oldest are so close in age they like to sit and quiz each other.
One recommendation: you may want to order one grade up from where your child is at for a challenge. Also, you can purchase trivia cards that deal exclusively with one subject. This is great if your child needs extra help in math or reading specifically.
You can find these in store at Barnes and Noble, or you can order them at Amazon for $8.76, with free super saver shipping. I even found these lately at a discount bookstore here in NYC for $4 each- so if you have a discount bookstore nearby try that out.