"Extra Credit" by Andrew Clements

Abby's grades are failing, and her teachers inform her she's got to repeat 6th grade. How embarrassing, can it get any worse? There's only one way to redeem herself, a special extra credit project. Abby is assigned a penpal in Afghanistan, a boy named Sadeed. They exchange letters and learn about each other's lives. Abby is addicted to rock climbing, but lives in flat Illinois. Sadeed lives among some of the world's highest mountains, yet focuses on his studies and helps out with his family's business. They develop a special friendship even though their countries are thousands of miles apart.