The Lemonade War (Lemonade War Series, BK. 1)

Fourth-grader Evan Treski is people-smart. He's good at talking with people, even grownups. His younger sister, Jessie, on the other hand, is math-smart, but not especially good with people. So when the siblings' lemonade stand war begins, there really is no telling who will win - or even if their fight will ever end. Brimming with savvy marketing tips for making money at any business, definitions of business terms, charts, diagrams, and even math problems, this fresh, funny, emotionally charged novel subtly explores how arguments can escalate beyond anyone's intent.