It's a paradox school administrators know all too well: Having fewer students in a school doesn't necessarily make it less expensive to run. Records from Alachua County Public Schools show that, in most cases, the most underpopulated schools have the highest per-pupil costs. School officials agree the figures show the use of building space is often inefficient. But that's where the agreement ends. Superintendent Carlee Simon said the figures justify her push for a comprehensive rezoning that would redistribute the student population, which she concedes will be controversial and may force some students to attend different schools. But some School Board members say the figures could bolster their argument that some schools that have hemorrhaged students should simply be closed — and that could be controversial as well.