KAKUMA, Kenya—A sea of 76 students in bright violet uniforms with pointed white collars confronted Jessica Deng as she stepped into her classroom. The students – all girls in the eighth grade – crowded around worn wooden desks and battered textbooks as she briskly set them to work on a math problem calculating the speed of someone who travels 80 kilometers in 4 hours. The equatorial sun had begun to heat up the September day and burned through the curtainless…