Sometimes school is so inconvenient where it comes to making money. Sources tell us Kendall Jenner, 15, the Kardashians’ half-sister, has been forced to miss a planned $20,000 appearance at this evening’s Fashion’s Night Out because she couldn’t get out of school in Los Angeles. An insider told us, “Kendall was offered $20,000 to host an event. She was interested but she had to back out because she couldn’t get out of school.” While it is unusual for reality to get in the way of a Kardashian money-spinning idea, sources tell us mom Kris Jenner is insisting Kendall complete her studies. Meanwhile her older sisters Kim, Kourtney and Khloe have been busy on the promotional trail. A Kardashian rep didn’t get back to us.