The Lemonade War by Jacqueline Davies

A wonderful series starts with a great book. The Lemonade War is book one in a four book series about siblings Jessie and Evan Treski. Jessie recently completed 2nd grade and was double promoted to 4th grade. She gets to skip 3rd grade .... how cool is that? Her brother Evan doesn't think it is so cool, HE is going into 4th grade, how can his kid sister be in his class? The week before school starts Jessie and Evan have a fight and decide to settle it by having a Lemonade War - who can make $100 in 5 days? We join the siblings on their wild 5 day adventure of trying to outdo each other and win the war.  Jessie and Evan are very close and do everything together, but not now. Neither one of them really remembers why they started the war, but someone has to win - right? If you enjoy book one don't forget to pick up the rest of the series, The Lemonade War books.