Helping struggling teachers improve has become a big concern–and a big business–across the country, especially as more states, including New York, introduce more rigorous teacher evaluations, says the Hechinger Report. The federal government gives local districts more than $1 billion annually for training programs. New York City schools spent close to $100 million last year just on private consultants. Yet even as districts increase accountability for teachers, few are checking on the companies, universities and in-school programs that are supposed to help them get better. On-the-job training for teachers, known as professional development, encompasses everything from day-long seminars, coaching provided by in-school specialists, courses in subjects like math and reading, and teachers working with one another to improve their skills. New York City even offers [1] Yoga and dance classes to its teachers. Yet little reliable, independent research exists on what kind of training for teachers actually works…