Teacher Quality Doesn't Significantly Impact Outcomes

Teacher quality is the single most underrated driver of student success, as proven by Chetty, Friedman, and Rockoff's landmark study of 2.5 million students: replacing a below-average teacher with an average one boosts lifetime earnings by $250,000 per classroom. This effect dwarfs class size reductions, which yield only 10% of the gain, and outperforms #9 because teacher impact compounds across years while multitasking habits only hurt the individual. A high-impact teacher in third grade alone closes 30% of the income-achievement gap. Dismissing teacher influence as negligible ignores a 10% test-score improvement annually, making this myth the costliest on the list for long-term economic mobility.