What the latest reading study that's getting a lot of buzz says – and where its evidence falls short

In early April 2023, I started getting emails and messages urging me to take a look at a fresh reading study in Colorado. The study, a working paper that has not yet been peer-reviewed, came to two dramatic conclusions. The first was that elementary school students who attended “Core Knowledge” schools – which teach young children a broad core curriculum in many subjects – were better readers. Their reading scores in third through sixth grades indicate that these children were not only above average at deciphering the words on the page but were better at understanding and analyzing what they were reading. Even more surprising was the finding that the reading gains were so large for low-income students that they would eliminate the achievement gap between rich and poor children. 

The nine authors, most of whom hail from the University of Virginia, issued a press release trumpeting it as the first long-term study of a knowledge-rich curriculum and the first to show outsized gains on state assessments. They said the gains were large enough to catapult U.S. reading achievement from 15th place among 50 nations on an international reading test of fourth graders to the top five. Robert Pondiscio, writing on the website of the conservative Thomas B. Fordham Institute, called it “compelling evidence” for the theories of University of Virginia English professor emeritus E.D. Hirsch, who developed the curriculum used in these schools and whose 1987 book Cultural Literacy inspired the common core standards movement in American education. Journalist Natalie Wexler, author of the 2019 book “The Knowledge Gap,” said the study ought to spark a re-evaluation of the usual approach to reading comprehension in schools, which frequently focuses on skills, such as asking students to find the main idea and make inferences. Hirsch’s Core Knowledge curriculum teaches skills too, but it places more emphasis on expanding children’s knowledge of the world, from Greek mythology to the solar system.

For advocates of building children’s general knowledge, the study is certainly positive news and an indication that this type of instruction may be beneficial. But from my perspective, it falls far short of convincing proof or vindication. For starters, the study took place at nine charter schools in Colorado, stretching from Denver to Fort Collins. It’s impossible from the study design to distinguish whether the Core Knowledge curriculum itself made the difference or if it could be attributed to other things that these charter schools were doing, such as teacher training or character education programs.

The schools catered to middle and upper income families; median family income exceeded $114,000 at three of the suburban schools. Only one of the schools had a somewhat lower income population, but median family income still exceeded $50,000 and fewer than a third of the children were living below the poverty line, not nearly as poor as many city schools. The claim of closing the achievement gap is based on only 16 students who attended this one charter school.

Researchers have long found correlations between a child’s knowledge and reading scores, but that’s not the same as proving that building knowledge first is what causes reading comprehension to flourish later. The theory – widely accepted by education researchers –  is that what we grasp from what we read depends on whether we can hook it to concepts and topics that we already have some knowledge about. Laboratory studies have found that children who are familiar with a topic are better able to comprehend a new reading passage on it. In one 1987 experiment, kids who were familiar with baseball were better able to retell a story they had read about a baseball game than children who had stronger reading abilities. 

However, U.S. schools, especially those that serve low-income children, have moved in the opposite direction. Educators have felt pressure to cut time for science, social studies and the arts in order to carve out more time for reading and math, the two subjects that are tested annually by every state and by which schools are judged. During reading class time, many schools emphasize skills over content, asking children to practice comprehension strategies on short reading passages, rather than reading a whole novel. Critics say this has hampered the ability of children to build a strong foundation of background knowledge at school and has impeded their reading comprehension.

“The major factor that’s the cause of achievement differences in low and high income students turns out to be their level of general knowledge,” said David Grissmer, a research professor at the University of Virginia and one of the lead authors of the study. “It’s geography; it’s history; it’s science; it’s cooking; it’s athletics, whatever that broad knowledge is about the world we live in. It comes from lots of different sources, sometimes from families, sometimes communities, sometimes from school. It’s the experiences kids have that build that general knowledge, which really provides the particular advantage that we see for higher income kids. I don’t think it completely accounts for it, but it accounts for more of that difference than I think most of us ever thought.”

It’s nearly impossible to test different instructional approaches in real classrooms. Teachers can teach only one curriculum at a time – often after years of training and practice to implement it correctly – and so it’s not practical to randomly assign some children to learn a different way in the same school. One can study the students at schools that have adopted the Core Knowledge curriculum, but it’s hard to know if the students who attend these schools would have scored just as high in reading if they had been taught the usual way at a traditional public school. 

In this study, the researchers copied a method used by charter school researchers. They identified nine charter schools in Colorado that had adopted Hirsch’s Core Knowledge curriculum. They were popular schools with more applicants than seats and so the schools conducted lotteries to admit students. Researchers tracked students who won kindergarten seats in 2009 and 2010, and monitored their test scores through sixth grade, comparing them with students who also wanted to attend these schools but lost the lottery. The lottery losers attended a variety of other schools, from traditional public schools to private schools to other charter schools. Some postponed starting kindergarten that year. Students who attended one of the Core Knowledge charter schools for at least four years had much higher reading scores than lottery losers who did not attend, and the advantage lasted through at least sixth grade. 

A huge complication in this study was that Colorado families had applied to many schools as part of the state’s school choice system. Half of the approximately 1,000 lottery winners chose not to claim their kindergarten seats and opted to attend other schools. In other words, researchers lost half of their study subjects. We don’t know how these children would have fared had they attended the Core Knowledge schools. The results might have been different. 

In theory, knowledge building and reading achievement ought to be a virtuous circle, where children with greater background knowledge should be able to grasp more of what they are reading, which, in turn, helps them learn more and build more background knowledge and become even better readers. However, in this study, researchers detected the full benefit of the Core Knowledge curriculum immediately in third grade, the first year that children are tested at schools. The advantage for Core Knowledge students did not increase further in fourth, fifth and sixth grades.

More than 600 schools across the United States have adopted all or parts of the Core Knowledge curriculum, according to the Core Knowledge website, and, what we all want to know, is how well it’s working in low-income public schools. As those results come in, it will be a welcome addition to the debate on how to teach reading, which, in my opinion, has been excessively focused on teaching phonics to children in kindergarten and first grades. That’s important, but becoming a good reader, with strong comprehension skills, takes a lot more. What kids need to know may prove to be critical. Of course, it will open up a whole new political debate of what content knowledge kids should be taught, and in our political times, that won’t be easy for communities to sort out. Procedures and strategies are easier. Content is hard.

The study, “A Kindergarten Lottery Evaluation of Core Knowledge Charter Schools: Should Building General Knowledge Have a Central Role in Educational and Social Science Research and Policy?” was funded by the Institute for Education Research (an arm of the U.S. Department of Education), the National Science Foundation and two private foundations. One of them, the Arnold Foundation, is among the many funders of The Hechinger Report.  

This story about reading comprehension was written by Jill Barshay and produced by The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education. Sign up for Proof Points and other Hechinger newsletters.