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Over the past decade, a majority of states have passed new “science of reading” laws or implemented policies that emphasize phonics in classrooms. Yet the 2024 results of an important national test, released last month, showed that the reading scores of elementary and middle schoolers continued their long downward slide, hitting new lows.

The emphasis on phonics in many schools is still relatively new and may need more time to yield results. But a growing chorus of education advocates has been arguing that phonics isn’t enough. They say that being able to decode the letters and read words is critically important, but students also need to make sense of the words. 

Some educators are calling for schools to adopt a curriculum that emphasizes content along with phonics. More schools around the country, from Baltimore to Michigan to Colorado, are adopting these content-filled lessons to teach geography, astronomy and even art history. The theory, which has been documented in a small number of laboratory experiments, is that the more students already know about a topic, the better they can understand a passage about it. For example, a passage on farming might make more sense if you know something about how plants grow. The brain gets overwhelmed by too many new concepts and unfamiliar words. We’ve all been there. 

A ‘Knowledge Revival’

A 2025 book by 10 education researchers in Europe and Australia, “Developing Curriculum for Deep Thinking: The Knowledge Revival,” makes the case that students cannot learn the skills of comprehension and critical thinking unless they know a lot of stuff first. These ideas have revived interest in E.D. Hirsch’s Core Knowledge curriculum, which gained popularity in the late 1980s. Hirsch, a professor emeritus of education and humanities at the University of Virginia, argues that democracy benefits when the citizenry shares a body of knowledge and history, which he calls cultural literacy. Now it’s a cognitive science argument that a core curriculum is also good for our brains and facilitates learning. 

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The idea of forcing children to learn a specific set of facts and topics is controversial. It runs counter to newer trends of “culturally relevant pedagogy,” or “culturally responsive teaching,” in which critics contend that students’ identities should be reflected in what they learn. Others say learning facts is unimportant in the age of Google where we can instantly look anything up, and that the focus should be on teaching skills. Content skeptics also point out that there’s never been a study to show that increasing knowledge of the world boosts reading scores.

It would be nearly impossible for an individual teacher to create the kind of content-packed curriculum that this pro-knowledge branch of education researchers has in mind. Lessons need to be coordinated across grades, from kindergarten onward. It’s not just a random collection of encyclopedia entries or interesting units on, say, Greek myths or the planets in our solar system. The science and social studies topics should be sequenced so that the ideas build upon each other, and paired with vocabulary that will be useful in the future. 

The big question is whether the theory that more knowledge improves reading comprehension applies to real schools where children are reading below grade level. Does a content-packed curriculum translate into higher reading achievement years later?

Putting knowledge to the test

Researchers have been testing content-packed lessons in schools to see how much they boost reading comprehension. A 2023 study of the Core Knowledge curriculum, which was not peer reviewed, received a lot of buzz. The students who attended nine schools that adopted the curriculum were stronger readers. But it was impossible to tell whether the Core Knowledge curriculum itself made the difference or if the boost to reading scores could be attributed to the fact that all nine schools were highly regarded charter schools and were doing something else that made a difference. Perhaps they had hired great teachers and trained them well, for example. Also, the students at these charter schools were largely from middle and upper middle class families. What we really want to know is whether knowledge building at school helps the poorest children, who are less likely to be exposed to the world through travel, live performances, and other experiences that money can buy.

Another content-heavy curriculum developed by Harvard education professor James Kim produced a modest boost to reading scores in a randomized controlled trial, according to a paper published in 2024. Reading instruction was untouched, but the students received special science and social studies lessons that were intended to boost young children’s knowledge and vocabulary. Unfortunately, the pandemic hit in the middle of the experiment and many of the lessons had to be scrapped. 

Related: Slightly higher reading scores when students delve into social studies, study finds

Still, for the 1,000 students who had received some of the special lessons in first and second grades, their reading and math scores on the North Carolina state tests were higher not only in third grade, but also in fourth grade, more than a year after the knowledge-building experiment ended. Most of the students were Black and Hispanic. Forty percent were from poor families.

The latest study

The Core Knowledge curriculum was put to the test in another study by a team of eight researchers in two unidentified cities in the mid-Atlantic and the South, where the majority of children were Black and from low income families. More than 20 schools had been randomly assigned to give kindergarteners some lessons from the Core Knowledge curriculum. The schools continued with their usual phonics instruction, but “read aloud” time, when a teacher ordinarily reads a picture book to students, had been replaced with units on plants, farming and Native Americans, for example. More than 500 kindergarteners looked at pictures on a large screen, while a teacher discussed the topics and taught new vocabulary. Additional activities reinforced the lessons. 

According to a paper published in the February 2025 issue of the Journal of Education Psychology, the 565 children who received the Core Knowledge lessons did better on tests of the topics and words that were taught, compared with 626 children who had learned reading as usual and weren’t exposed to these topics. But they did no better in tests of general language, vocabulary development or listening comprehension. Reading itself was not evaluated. Unfortunately, the pandemic also interfered in the middle of this experiment and cut short the analysis of the students through first and second grades.  

Related: Inside the latest reading study that’s getting a lot of buzz

Lead researcher Sonia Cabell, an associate professor at Florida State University, says she is looking at longer term achievement data from these students, who are now in middle school. But she said she isn’t seeing a clear “signal” that the students who had this Core Knowledge instruction for a few months in kindergarten are doing any better. 

Glimmers of hope

Cabell did see glimmers of hope. Students in the control group schools, who didn’t receive Core Knowledge instruction, also learned about plants. But the Core Knowledge students had much more to say when researchers asked them the question: “Tell me everything you know about plants.” The results of a test of general science knowledge came just shy of statistical significance, which would have demonstrated that the Core Knowledge students were able to transfer the specific knowledge they had learned in the lessons to a broader understanding of science. 

“There are pieces of this that are promising and encouraging,” said Cabell, who says that it’s complicated to study the combination of conventional reading instruction, such as phonics and vocabulary, with content knowledge. “We need to better understand what the active ingredient is. Is it the knowledge?” 

All the latest Core Knowledge study proves is that students are more likely to do well on a test of something they have been taught. Some observers errantly interpreted that as evidence that a knowledge rich curriculum is beneficial. 

Related: Learning science might help kids read better

“If your great new curriculum reads articles about penguins to the kids and your old stupid curriculum reads articles about walruses to them, one of these is going to look more successful when the kids are evaluated with a penguin test,” explained Tim Shanahan, a literacy expert and a professor emeritus at the University of Illinois at Chicago who was not involved in this research.

Widening achievement gaps

And distressingly, students who arrived at kindergarten with stronger language skills absorbed a lot more from these content-rich lessons than lower achieving students. Instead of helping low achieving kids catch up, achievement gaps widened.

People with more knowledge tend to be better readers. That’s not proof that increasing knowledge improves reading. It could be that higher achieving kids like learning about the world and enjoy reading. And if you stuff a child with more knowledge, it’s possible that his reading skills may not improve.

The long view

Shanahan speculates that if knowledge building does improve reading comprehension, it would take many, many years for it to manifest. 

“If these efforts aren’t allowed to elbow sound reading instruction aside, they cannot hurt and, in the long run, they might even help,” he wrote in a 2021 blog post.

Researchers are still in the early stages of designing and testing the content students need to boost literacy skills. We are all waiting for answers.

Contact staff writer Jill Barshay at 212-678-3595 or barshay@hechingerreport.org.

This story about Core Knowledge 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.