“Jill Barshay writes the weekly “Proof Points” column about education research and data, covering a range of topics from early childhood to higher education. She taught algebra to ninth-graders for the 2013-14 school year. Previously, Barshay was the New York bureau chief for Marketplace, a national business show on public radio stations. She has also written for Congressional Quarterly, The Wall Street Journal, The New York Times and the Financial Times, and appeared on CNN and ABC News.“

The idea that teachers stop getting better after their first few years on the job has become widely accepted by both policymakers and the public. Philanthropist and former Microsoft CEO Bill Gates popularized the notion in a 2009 TED Talk when he said “once somebody has taught for three years, their teaching quality does not change thereafter.” He argued that teacher effectiveness should be measured and good teachers…