A charter school boss runs the numbers (via the WaPo):
At Harlem Success Academy Charter School, where we’ve gotten some of the best results in New York City, some classes are comparatively large because we believe our money is better spent elsewhere. In fifth grade, for example, every student gets a laptop and a Kindle with immediate access to an essentially unlimited supply of e-books. Every classroom has a Smart Board, a modern blackboard that is a touch-screen computer with high-speed Internet access. Every teacher has a laptop, video camera, access to a catalogue of lesson plans and videotaped lessons.
Outfitting a classroom this way costs about $40,000, or $13,500 amortized over three years. That’s how much New York charter schools receive per pupil annually, so we can afford this by just increasing class size by a single student. .. In other words, a 19th-century school can be transformed into a well-managed 21st-century school by adding just two students per classroom. Reducing class size is expensive because most costs vary with class size. Decrease a class from 25 to 24 students and you need to hire 4 percent more teachers as well as build and maintain 4 percent more buildings.
Obsession with class size is causing many public schools to look like relics. We spend so much to employ lots of teachers that there isn’t enough left to help these teachers be effective. According to the city’s education department, New York public schools spend on average less than 3 percent of their budgets on instructional supplies and equipment (1 percent), textbooks (0.6 percent), library books and librarians (0.5 percent), and computer support (0.5 percent). Basic supplies are rationed in absurd ways: A school will pay $5 million in salaries to teachers who end up wasting time writing on blackboards because the school has run out of paper that costs a penny a page. (Don’t believe me? Ask a teacher.)
Also, class sizes would not need to be as small if teachers were better trained in classroom management skills. Here is a bit from a must-read NYTimes magazine piece on the topic:
By figuring out what makes the great teachers great, and passing that on to the mass of teachers in the middle, he said, “we could ensure that the average classroom tomorrow was seeing the types of gains that the top quarter of our classrooms see today.” He has made a guess about the effect that change would have. “We could close the gap between the United States and Japan on these international tests within two years.”