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Building students’ general knowledge can lead to dramatic long-term improvements in reading comprehension, a new study suggests—casting serious doubt on standard teaching approaches.

rigorous study involving more than 2,000 students has found that children who got a content-rich, knowledge-building curriculum for at least four years, beginning in kindergarten, significantly outperformed their peers on standardized reading comprehension tests. Students from low-income families made such dramatic gains that their performance on state tests equaled that of children from higher-income families.

To understand the significance of these findings, it’s important to have some background information. For at least the past 25 years, reading scores in the U.S. have been largely stagnant, with about two-thirds of students scoring below proficient on national tests. Gaps between students at the upper and lower ends of the socioeconomic spectrum have remained wide and by some estimates have grown significantly, despite massive efforts to narrow them.

In response to low scores, schools have intensified instruction in reading, which includes the ability to decipher individual words. Over the past few years there’s been a push to bring that aspect of reading instruction in line with scientific evidence showing the need for systematic instruction in phonics.


Reading Comprehension Instruction Focuses on Skills

But most of the time spent on reading is devoted to reading comprehension, which is what state and national tests purport to measure. The standard approach is to focus on comprehension skills and strategies, like “finding the main idea” of a text and “making inferences.”

Students practice the skills on  books—fiction, or nonfiction on random topics—that have been determined to match their individual reading levels. The goal is not for children to acquire any substantive knowledge but rather to master skills that will theoretically enable them to understand the complex texts they’ll be expected to read in the future.

Over the last several years, an increasing number of schools have shifted to elementary literacy curricula that systematically build children’s knowledge and vocabulary while also providing the kind of phonics instruction backed by science. But the trend towards knowledge-building hasn’t gained as much traction as the movement for systematic phonics.

One reason may be that we haven’t had strong experimental evidence for knowledge-building. We do have lots of evidence showing that readers who have relevant knowledge—either of the topic they’re reading about, or of general academic vocabulary—have better comprehension. That evidence supports the idea that students from higher-income families generally do better on reading tests because they’re better able to pick up academic knowledge outside of school. But it’s been harder to demonstrate that building knowledge leads to better comprehension.

That’s because the tests generally used to measure the success of a knowledge-building intervention rely on reading passages on topics that haven’t been covered in the intervention. It can take a long time for students to acquire the level of general knowledge that improves their ability to understand passages on topics they haven’t learned about. But studies of the effects of knowledge-building on reading comprehension have generally lasted a year or less.


The Colorado Study

That brings us to the long-awaited multi-year study released last week, conducted by researchers at the University of Virginia. The experiment took advantage of the fact that Colorado has long had an unusual number of elementary schools that use a knowledge-building curriculum. Researchers focused on nine such schools in the Denver area that have more applicants than seats, requiring them to conduct lotteries for kindergarten admission. That allowed researchers to compare a “treatment group”—children who got in through the lotteries—with a “control group” consisting of children who applied but didn’t get in.

More than 500 children admitted through the lottery got a curriculum based on the Core Knowledge Sequence. Rather than putting comprehension skills in the foreground, the Sequence immerses children in rich content in history, geography, science, and other subjects, largely through having teachers read texts aloud and lead class discussions.

The various knowledge-building curricula developed in recent years all cover different topics in different ways, but they all share Core Knowledge’s focus on content. Instead of jumping rapidly from one topic to another, students spend several weeks learning about each topic. They also read and write about the content covered in the core curriculum rather than random, unconnected topics. Previous studies have measured the results of some of these curricula, including CKLA, after one or two years and found a positive but modest effect.

Researchers conducting the Colorado study waited four years, until the children reached third grade—the first year state standardized tests are given—before measuring the results. They continued to look at test scores for those students, and their peers who failed to win the lottery, through sixth grade.

They found that the treatment group as a whole experienced significant gains on reading tests in each grade compared to the control group. In fact the gains were large enough that, if translated to American students as a whole, the U.S. would move up to a position among the top five countries on an international reading test given to fourth-graders. Currently, it ranks 15th out of the 58 countries that participate.


Gap-Closing Gains for Students From Low-Income Families

Breaking down the study’s results by income level leads to additional insights. Eight of the nine schools were located in middle- to high-income areas. Even though those children were presumably acquiring a fair amount of academic knowledge at home, they still benefited from acquiring knowledge at school. The effect size—which measures the difference between their performance and their respective control groups—was 0.445.

In the Colorado study, the effect size for students at the one school in a low-income area was truly extraordinary: 1.299. They also got large boosts in math scores and on the state science test given to fifth-graders. In fact, their gains were so large that, according to the researchers, they eliminated the gaps on Colorado tests between students from low- and high-income families, in all three subjects.

The study has not yet been peer-reviewed or published, but the data have been subjected to rigorous evaluation. Still, some caveats are in order. Most significantly, the data from the school in a low-income area was based on only 16 students. And we don’t know the income levels of those students’ families since the researchers were relying on data on the average income level in the school district as a whole.

In any event, one study can never be definitive. It would be nice to have data from more long-term studies like the Colorado one. But given all the other evidence we have—both of the potential benefits of knowledge-building curricula and the clear failings of the current approach—we shouldn’t wait until before taking action. We’ve already done enough damage to children’s prospects—albeit with the best of intentions—and we can’t afford to prevent millions more students from reaching their full potential.


This post draws on an article by the author that originally appeared on


Natalie Wexler is an education writer and the author of The Knowledge Gap: The Hidden Cause of America’s Broken Education System—And How to Fix It (Avery 2019). She is also the co-author, with Judith C. Hochman, of The Writing Revolution: A Guide to Advancing Thinking Through Writing in All Subjects and Grades (Jossey-Bass, 2017), and a senior contributor to the education channel on Her newsletter, Minding the Gap, on Substack, is available for free.

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