The Lemonade War, by Jacqueline Davies, 2007

It was the letter from the school that ruined Evan’s summer and turned his friendship with Jessie, his younger sister, sour. Their lemonade-stand hobby turns into a fierce end-of-summer rivalry to see who can earn the most money selling lemonade before Labor Day. But there’s more at stake than just the money. Engaging middle-grade realism told from dual points of view. Recommended.