I bought the bundle of four dragon box apps this summer, and I told my 4 year old son that we could start Algebra 5+ after he finished Numbers (which was fantastic too). We have been playing 5+ for about a week now, and he loves it. He asks everyone who visits to "play algebra" with him, but at this point he doesn't really need the help. When we play together I just ask him "where should we start?" and he takes it from there, saying things like "should we simplify this fraction first?" or "f over f equals one whole, so these cards are unnecessary." Wow. Highly recommended for adults too who might, like me, need a reminder of how algebra works before teaching their 4 year old.