At Batasan Hills National High School in the Philippines, every inch of space is used meticulously. Classrooms have been divided in half to make way for extra groups of students and there are designated entry points and passing lanes to accommodate the crowds in between lessons. Even the space under the staircases is not wasted: it’s here, below the sloped ceiling, with no natural light, that teachers cram together to plan lessons and hold faculty meetings. It’s not, however, enough to fully accommodate the intake of 18,638 students, so instead, the school has resorted to running two shifts, with some...