Researchers of varying views have come to agree that, of factors that schools can control, teachers make the largest difference in a student’s education. Teacher quality scholar Dan Goldhaber has succinctly asserted, "It appears that the most important thing a school can do is to provide its students with good teachers." Stanford University’s Eric Hanushek and colleagues have conducted several rigorous studies to measure the impacts that teachers have on students and have repeatedly found that teachers matter. Asserting that teachers have profound effects on student achievement, Hanushek and Steven Rivkin wrote, "[A] good teacher will get a gain of 1.5 grade level equivalents while a bad teacher will get .5 year for a single academic year." These researchers have also found that effects of teachers last over time; they estimate that "having five years of good teachers in a row (1.0 standard deviation above average, or at the 85th percentile) could overcome the average seventh-grade mathematics achievement gap between lower-income kids (those on the free or reduced-price lunch program) and those from higher-income families."
Although she differs from Hanushek in her views over which characteristics of teachers make them more effective, Stanford’s Linda Darling-Hammond agrees that high-quality teachers are important for student success. In turn, political scientist Terry Moe of the Hoover Institute, a scholar who does not regularly concur with Darling-Hammond, also asserts that teachers are essential. In an article suggesting that collective bargaining interferes with providing students with good teachers, Moe writes, "When contract rules make it difficult or impossible to weed out mediocre teachers, for example, they directly undermine the single most important determinant of student learning: teacher quality."