Bill Gates claimed in his TED talk Mosquitos, malaria and education:

A top quartile teacher will increase the performance of their class -- based on test scores -- by over 10 percent in a single year. What does that mean? That means that if the entire U.S., for two years, had top quartile teachers, the entire difference between us and Asia would go away.

Is the difference between the teaching results of top quartile teachers big enough, so that if all teachers in the US would teach at that level and if the teaching quality in Asia would be held constant, the increased teaching quality would close the gap between educational achievement between the US and Asia within 2 years?

  • 1
    May we change this question to be about the correlation between top-quartile students and the 10% boost in test scores? The current question seems a little bit too counterfactual speculation for my taste. If my grandma had wheels...
    – Oddthinking
    Dec 31, 2016 at 0:52
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    @Oddthinking The problem with focusing on 10% increase in test scores per year is that it depends on how the test is structured. It's not obvious how much 10% happens to be. The second sentence tries to translate the number into a real world comparison. Are two years with 10% performance per year increase roughly the difference between the US and Asia? Apart from that you leave out the "per year"-part of the claim in your comment, which is important.
    – Christian
    Dec 31, 2016 at 9:53
  • @Christian maybe we should focus the question on whether the disparity between US and china is about 20%. This would leave out the icky part, give Gates the benefit of the doubt (good intentions, bad logic), and still verify important evidence.
    – Sklivvz
    Dec 31, 2016 at 12:13
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    Yong Zhao an education researcher at the University of Oregon in Eugene says “Standardised tests reward the ability to find answers to pre-existing questions, but finding the question is more important”-newscientist.com/article/…. I like to add that finding newer answers to pre-existing questions or asking newer questions to find better answers are important factors in determining creativity and initiatives of students rather than fixating on teaching quality or international tests. Jan 3, 2017 at 12:43
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    The difference in education between Asia and USA is not quality, but selection. Secondary and tertiary education in China is allowed based on entry tests, but in the USA entry is universal. Combined with the fact they have 3 times the population, no wonder they appear smarter.
    – user11643
    Dec 21, 2017 at 17:41

1 Answer 1



  1. In USA, teachers with stronger credentials tend to teach in schools with more advantaged and higher performing students.

Nationally, there is “abundant evidence that teachers with stronger credentials tend to teach in schools with more advantaged and higher performing students and, to a far lesser extent, that similar matching occurs across classrooms within schools:” Source: FACT SHEET – TEACHER EQUITY

  1. The caliber of teachers is found to impact the student achievement in certain schools.

The disparity between the caliber of teacher found in a high-poverty or high-minority school and that of a teacher found in a low-poverty or low-minority school has a massive impact on student achievement. “If the effects were to accumulate, having a top-quartile teacher rather than a bottom- quartile teacher four years in a row would be enough to close the black-white test score gap.” Source: FACT SHEET – TEACHER EQUITY.

This also shows that four years in row are required for top quartile teachers to close the gap between black and white educational test scores in USA which is certainly more than the two years claimed by Bill Gates to close the gap between Asia and USA if one employs only top quartile teachers in USA.

Moving up (or down) 10 percentile points in one year is a massive impact. For some perspective, the black-white achievement gap nationally is roughly 34 percentile points. Therefore, if the effects were to accumulate, having a top-quartile teacher rather than a bottom-quartile teacher four years in a row would be enough to close the black-white test score gap. Source: Identifying Effective Teachers Using Performance on the Job

  1. Quality teachers do make a difference and deliver improvement in student learning.

Rather, the key message to be gained from the educational effectiveness research cited above, is that quality teachers and their professional development do make a difference, and that it is not so much what students bring with them that really matters, but what they experience on a day-to-day basis in interaction with teachers and other students in classrooms. Teachers can and do make a difference and that consistent high-quality teaching, supported by strategic professional development, can and does deliver dramatic improvements in student learning. Source: The Importance of Teacher Quality as a Key Determinant of Students’ Experiences and Outcomes of Schooling.

  1. Teachers tend to differ in effectiveness.

Summarizing the material reviewed, we see that teachers matter and differ in effectiveness. The most important influence on individual differences in teacher effectiveness is teachers’ general cognitive ability, followed by experience and content knowledge. Masters’ degrees and accumulation of college credits have little effect, while specific coursework in the material to be taught is useful, particularly in more advanced subjects. Specific, curriculum-focused and reform-centered professional development appears to be important to effective instruction. Context studies tell us that all teachers can do a better job when supported by good curriculum, good schools, and good state policy. Source: Scientifically Based Research on Teacher Quality: Research on Teacher Preparation and Professional Development

First, there is wide variation in the effectiveness of teachers, even after adjusting for student characteristics such as baseline test performance, race/ ethnicity, family income, gender, and so on. Source: Identifying Effective Teachers Using Performance on the Job

  1. Research from Australia shows that there are other factors which affect school performance which is actually not taken into account for Bill Gate's claim about USA.
  1. Previous student attainment (in Victoria they use GAT scores to measure this): This is used to ensure that you are measuring the ‘value added’ to students’ performance, not just their final achievement
  2. Socio Economic Status of the student intake: This is used to remove bias from a school being in a particular area which may affect it’s student intake. For example, if a school is located in an area with a higher proportion of social housing, statistically the students are likely to be less engaged with education (eg higher absence rates), with less well educated parents.
  3. School size, based on number of students: OECD research quoted in the report shows that as school size falls below 1,000 students, average student attainment falls too
  4. Rural/Urban location Research shows that this is an important influencer of school performance within Australia
  5. School sector – Public, Private or Catholic When you don’t take this factor into account, then the analysis of school performance tends to show schools grouping into three bands, representing the different sectors. Source: The 5 factors which affect school performance

TL;DR: Research evidence shows that teachers are certainly contributing to student learning.

General Importance of Quality Teaching: The two strongest in-school influences on student learning are teaching and school leadership, the latter to a lesser extent. The year-long and cumulative effects on student achievement of having a qualified teacher can be measured and have been found to be substantial. Source: Improving Student Learning By Supporting Quality Teaching

However we are unsure to what degree the effect actually is since it is difficult to measure teachers’ contributions to student learning with a high degree of certainty (high confidence levels). We also are not sure whether such gains related to the teacher or his/her methods, to other sources such as school factors, nonschool factors mentioned here, or merely to chance.

In some studies, factors that would logically be related to student achievement may appear to be only weakly related or not related at all. It might be a sample size issue because smaller sample sizes make it difficult to determine effects. Or it could be that the logic is wrong. But it also could be that the measurement tools and statistical analyses being conducted are not sensitive or precise enough to capture the effects. For example, statewide standardized student achievement tests are not ideal for measuring the effects of changes in instructional practice. Given that such tests occur once a year in most states and that teachers have the students in their classrooms for only six or seven months before the tests, subtle but important changes in practice may not show up as effects on achievement test scores. Source: The Link Between Teacher Quality and Student Outcomes: A Research Synthesis

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