MAHAMAT RAMADANE IN a makeshift open-air classroom, dozens of children sat squeezed together on a mat and watched as their teacher chalked simple sums on a blackboard - a rare chance of education for their nomadic community in Chad. Around 7% of the central African nation's population of about 16 million are nomads, who move hundreds of kilometres from the south with their herds every year when seasonal rains turn the semi-arid central regions green with fresh pasture. This way of life is centuries-old but incompatible with Chad's formal education system. According to the Copenhagen-based International Work Group for Indigenous…