Pencils, pens, crayons, construction paper, T-shirts, snacks and, sometimes, a pair of shoes: The costs add up for public school teachers who reach into their own pockets for classroom supplies, ensuring their students have the necessities of learning. Nearly all teachers are footing the bill for classroom supplies, an Education Department report found, and teachers in high-poverty schools spend more than those in affluent schools. The report, prepared by the National Center for Education Statistics and released Tuesday, is based on a nationally representative survey of teachers during the 2015-2016 school year.