Over the past thirty years, per-pupil spending on education has doubled. Almost half of this increase was caused by the hiring of many more teachers. As a result, the number of students per U.S. teacher has shrunk from 22 to 15 since the early 1970s. Oddly, this hasn't led to a reduction in class size; instead, the average teacher simply faces fewer classes per day. Why has the additional money been channeled into more teachers teaching fewer classes? According to the Manhattan Institute's Jay Greene and Greg Forster, the ones who benefit the most from this arrangement are the teachers' unions; by jacking up the total number of teachers, they collect more dues and enlarge the ranks of shock troops they can call on to volunteer at election time.
"Widespread exploitation," by Jay Greene and Greg Forster, National Review Online, February 10, 2003