There IS Proof Knowledge Works. And It's Overwhelming.

Cognitive science has demonstrated repeatedly that knowledge is essential for making sense of texts. Suggesting otherwise is misleading—and potentially harmful to students who need it the most.

Jill Barshay of The Hechinger Report is one of the better education journalists working today. She does her homework, understands research, and makes a visible effort to connect evidence with real-world teaching. Her recent piece, “The buzz around teaching facts to boost reading is bigger than the evidence for it,” raised concerns about the empirical support for knowledge-rich curricula in improving reading comprehension. She wrote, “There’s never been a study to show that increasing knowledge of the world boosts reading scores.” Such a broad and sweeping statement is demonstrably incorrect, deeply misleading, and carries significant downside for reading instruction if taken uncritically. The issue is not a lack of compelling evidence—there is prodigious evidence—but rather the difficulty of isolating long-term curricular effects in research.

The story is not about the limits of knowledge-rich curriculum. It’s about the limits of research methods.

To begin, few (if any) proponents of knowledge-rich curricula advocate merely for “teaching facts.” That’s an unfortunate cartoon that has been used as a strawman by its opponents to mock and lampoon a knowledge-based approach to literacy, conjuring Thomas Gradgrind, the school superintendent in Dickens’ Hard Times who insists children must be taught to value facts over imagination and creativity. The case for a knowledge-rich approach is far more nuanced, rooted in extensive cognitive science research on how knowledge supports comprehension and critical thinking. Reductionist expressions such as “a content-packed curriculum,” or “content-heavy curriculum” do a disservice and fail to accurately capture what the ten international researchers who wrote Developing Curriculum for Deep Thinking: The Knowledge Revival are advocating. (The book provides the occasion for Barshay’s piece.)

Likewise, having praised and admired her work, it was hard not to wince at Barshay’s characterization of knowledge-rich curriculum as “forcing children to learn a specific set of facts and topics” or “stuff[ing] a child with more knowledge.” The book’s authors (and advocates of knowledge-rich education at large) make clear that they are referring to carefully and democratically selected, coherent, well-sequenced and interconnected knowledge—not rote memorization of large amounts of unrelated facts, let alone “forcing” anyone to learn them.

Contrary to the claim that there’s never been a study, Developing Curriculum for Deep Thinking synthesizes a wealth of evidence supporting the role of knowledge in learning. The book argues for a coherent curriculum that systematically builds students’ background knowledge to facilitate deeper understanding and better reading comprehension. This aligns with decades of research in cognitive science demonstrating that comprehension is not a transferable skill but is largely dependent on prior knowledge.

Barshay’s Hechinger piece presents several key arguments: first, while background knowledge is clearly important for comprehension, the evidence linking knowledge-rich curricula to improved reading outcomes is inconclusive; second, many studies showing an association between knowledge and comprehension are correlational rather than causal; and third, proponents of knowledge-building curricula may be overstating the strength of the empirical evidence supporting their approach.

It is important to clarify the distinction between correlational and causal studies. Correlational studies identify relationships between two variables—for example, students with more background knowledge tend to perform better in reading comprehension. However, these studies do not prove that knowledge directly causes better comprehension, as other factors may also be influencing the outcome. In contrast, causal studies attempt to establish a direct cause-and-effect relationship, often through experimental designs such as randomized controlled trials.

While her points are not entirely without merit, they risk missing the bigger picture. The nature of reading research makes it inherently difficult to isolate and prove with definitive causal evidence that specific curricular interventions lead to improved reading achievement. Reading comprehension is influenced by a complex interplay of factors, including vocabulary, background knowledge, and syntax, making it exceptionally tricky to conduct randomized controlled trials that can definitively attribute gains to a knowledge-rich curriculum alone. Moreover, the effects of knowledge-building approaches accumulate over years, not days, weeks or months, making short-term experimental studies inadequate for capturing their true impact.

Barshay herself quotes Tim Shanahan acknowledging that it would take many, many years for gains to manifest. Reading interventions are studied over weeks or months, whereas a knowledge-rich approach yields its most significant effects over years. The benefits of having broad background knowledge may not be immediately apparent, but they are crucial for long-term reading success. Moreover, an assistant professor sweating out tenure would likely not pursue such a study, given the pressures of publishing on shorter time frames. “It would take years to see a general effect [of knowledge-rich curriculum implementation],” University of Virginia cognitive scientist Dan Willingham explains. “That kind of research is very expensive and would only be undertaken by someone who doesn't need a quick research pay-off.”

“Whenever people elevate causal over correlational conclusions, I point out that if we insisted on a direct experiment, we would not know that smoking causes cancer,” observes Dylan Wiliam, one of the contributors to Developing Curriculum for Deep Thinking. In dwelling on the lack of “causal” evidence without the larger context, Barshay’s piece risks inadvertently downplaying the practical significance of building background knowledge as a foundation for reading comprehension, which is simply not in dispute. Cognitive science has demonstrated repeatedly that knowledge is not just helpful but essential for making sense of texts. Studies such as the well-known “Baseball Study” (Recht & Leslie, 1988) have shown that students with prior knowledge of a subject comprehend related texts far better than those without it, regardless of their general reading ability. This insight has been reinforced by scholars like Willingham and E.D. Hirsch Jr., who have argued that efforts to improve reading scores must go beyond strategy instruction and ensure that students acquire broad, domain-specific knowledge across subjects.

A useful comparison can be drawn to dieting and exercise. It might be challenging to show a direct cause-and-effect relationship between a specific weight loss and exercise program, but that does not mean the broader evidence for diet and exercise is lacking. We accept that long-term health outcomes are influenced by consistent, cumulative behaviors. Similarly, the impact of a knowledge-rich curriculum unfolds over time, making it difficult to capture its full effect in short-term studies or in a specific curriculum. This overall approach – less time spent looking in the mirror; more time directing students’ attention out of windows – is the thing.

Valorizing knowledge-rich curricula is a sensible response to decades spent focusing on reading “skills and strategies” that demonstrably fail to transfer to new and unfamiliar contexts. Recent meta-analytical research also suggests (not surprisingly) that the effects of reading strategy instruction is significantly strengthened by instruction in background knowledge (Peng et al., 2023). Moreover, an emphasis on “mirrors over windows”—prioritizing students' personal experiences in reading and writing—may offer a false positive. When students read and write about what they already know, they appear to be stronger readers and writers than they truly are, as the “Baseball Study” would predict. However, when faced with unfamiliar domains, their comprehension falters. This should underscore the importance of broad, structured knowledge-building rather than an overreliance on self-referential literacy activities.

For years, we have tried to raise reading achievement by teaching students “what good readers do”—encouraging them to adopt and emulate habits associated with effective reading. But this approach has fallen short because reading comprehension is not just a matter of habits; it depends on knowledge. Researchers like Micheline Chi and Derek Hodson made it clear that the way experts do science is not the best way for students to learn science. Similarly Paul Kirschner (2009) showed that the way knowledge is built in a field should not be mistaken for the best way to teach it. In sum, instead of merely teaching students what good readers do, knowledge-rich curriculum instills over time what good readers know.

This overweighted instructional focus on reading skills and strategies has led to what I have described elsewhere as “cargo cult reading”—a phenomenon where students mimic the behaviors of proficient readers without grasping the deeper mechanisms at work. Just as cargo cultists in the Pacific built imitation airstrips and control towers to lure planes to return and disgorge precious goods—emulating behaviors and routines they witnessed soldiers perform during World War II—many reading programs have students practice surface-level comprehension skills without ensuring they possess the knowledge necessary to that make comprehension occur.

Finally, citing a 2023 study of the Core Knowledge curriculum (a causal study) which was implemented to great effect in nine Colorado charter schools, Barshay wonders whether it was a result of the curriculum or other factors, particularly since “students at these charter schools were largely from middle and upper middle class families.” However there was one low-income school among the nine in that study. It showed even larger effects in ELA and measurable effects in math and science—gains large enough to eliminate the achievement gap associated with income.

The insinuation that a knowledge-rich curriculum is elitist, favoring the already advantaged, is particularly troubling. E.D. Hirsch Jr. has long countered this claim, emphasizing that access to broad, shared knowledge is a key mechanism for democratizing opportunity. In Cultural Literacy, Hirsch argues that when students from disadvantaged backgrounds are deprived of the same foundational knowledge that wealthier peers often acquire at home, they are placed at a permanent disadvantage. A knowledge-rich curriculum is not about privileging certain students but about ensuring that all students—regardless of background—have access to the cultural and intellectual capital needed to engage fully in civic and professional life. In a speech some years ago, Hirsch framed the matter eloquently. “It's my fervent belief, reinforced by everything I have learned from study and experience,” he concluded, “that public education has no more right to continue to foster segregated knowledge than it has to foster segregated schools.”

Let that be the first and last word on “equity.”

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