In his more upbeat moments, Stanford economist Eric Hanushek believes improving schools is possible and successful reform models exist to point the way.

However, he says, “When I wake up on the pessimistic side, I worry school success is very individual-specific, and we have not learned how to institutionalize this. We are depending on one leader, one governor, one mayor or one school superintendent, and that success follows this one person.”

A noted education scholar, Hanushek finds fresh cause for pessimism in a new study on the seeming immutability of  the achievement gap between low and high income students in the United States.

The study, which Hanushek co-authored with three other academics, including Paul Peterson, director of Harvard's Program on Education Policy and Governance, will appear Monday in Education Next, an education journal sponsored by the John F. Kennedy School of Government at Harvard University.

Using data from four respected assessments of student performance — including NAEP, the National Assessment of Educational Progress, TIMSS, the Trends in International Mathematics and Science Study, and PISA, the Program for International Student Assessment — the researchers reviewed 98 tests administered to 2.7 million students in a nearly 50-year span of time.

Their conclusion: A stark opportunity gap persists between America’s haves and have-nots, despite a nearly half century of state and federal attempts to provide poor children with extra resources to catch up. Yet, the gap hasn’t budged.

“We have been trying a lot of things to close that achievement gap over time, but these gaps have not changed one whit over the almost half-century in which we are able to track performance. The gap we saw in 1970 is the same gap we saw in 2015,” said Hanushek in a conference call with reporters last week and a follow-up phone interview afterward.

The achievement gap between kids at the highest and lowest socioeconomic levels is daunting — equivalent to three to four years of learning.

The stagnation crosses incomes. “We would feel better about these constant achievement gaps if all achievement were rising, so everybody was better off,” said Hanushek. “That is not what we saw.” While the test scores over time show fairly substantial gains in students at ages 13 and 14, those gains fade by age 17, which Hanushek blames on a lack of meaningful reinvention of high school.

Despite Head Start, desegregation, mandated services for students with disabilities and more equal funding between rich and poor school districts, nothing has ameliorated the social advantages wealthier kids bring to the classroom, said study co-author Paul Peterson.

“When I began this project, I thought the gap was closing,” said Peterson, “So, the question arises: Why hasn’t it gotten better? The simple answer is that nothing has changed out there that is relevant.”

The positive changes in the past half-century, including rising educational attainment by parents, may have been offset by a decline in teacher quality, suggest Peterson and Hanushek.

They maintain the quality of the teaching force — a key factor in student achievement — fell as women gained access to career opportunities outside of the classroom. The researchers cite a drop in the math and reading skills of teachers and decreasing rates of teachers graduating from selective colleges.

"When talented women have the opportunity to work in fields that reward them for their productivity, they are going to leave a field where they're not paid for their productivity," said Peterson. "The quality of the teaching profession has a particular effect on low socioeconomic students; those students are, unfortunately, encountering the most inexperienced teachers."

“While there is a lot of lip service that says we have to make our schools better and we have to get better teachers, we don’t pursue policy designed to actually do that,” said Hanushek.

“We are shirking the issue of teaching quality,” said Peterson. “There is no direct effort on a national scale to enhance the quality of the teaching profession.”

Despite more public skepticism around what test scores signify, Hanushek said, “Scores in these achievement tests are actually good measures of expected future incomes, so, if kids are unprepared for life, or at least for jobs and college, as seen by these test scores, they are going to have their own families of poor kids. That is the tragedy.”