How much knowledge is necessary for comprehension?

There’s an image I like to use when describing the role of prior knowledge and vocabulary in reading comprehension: Think of a reading passage like a game of Jenga, where you take turns removing one block at a time from a tower of blocks. Imagine that every one of those blocks is a bit of background knowledge or an essential vocabulary word. Pull out some number of blocks, and the tower still stands. Pull out one too many, and it collapses completely. All sense and meaning is lost.

But how many is too many? Can we predict with any certainty the point at which a lack of background knowledge and vocabulary is fatal to comprehension? A new study suggests there is a “knowledge threshold”—a point below which lack of background knowledge impedes understanding—and that it’s possible to predict whether students fall below or above it on a given topic.

An experiment was conducted by Tenaha O’Reilly, Zuowei Wang, and John Sabatini, and published in the journal Psychological Science, among a socioeconomically diverse set of about 3,500 high school students from thirty-seven schools in two states. It involved presenting students with a list of words—some related to the topic they were going to read about (in this case a passage about ecology); some unrelated—and asked the students to determine if each word was related to the topic or not. In short, students took two tests: a knowledge test, then a reading test. Using a sophisticated statistical analysis, the trio of researchers “were able to identify a quantifiable point (59 percent on the knowledge test) at which there was a qualitative change in the relationship between background knowledge and reading comprehension.”

That’s the knowledge threshold.

“We predicted that students’ performance in such a keyword-recognition test would be related to comprehension,” the authors note. And unsurprisingly, some words in the experiment were “more predictive of exceeding the knowledge threshold than others” (the words ecosystems, habitat, and species, for example). “This suggests that these might be words students must know in order to perform above the knowledge threshold,” the authors add. “Measuring students’ background knowledge before they read a text may reveal which students are likely to have a reading-comprehension problem and which may need to build additional background knowledge before reading,” they conclude. “But how much knowledge is too little? The answer to this question is complex but is likely discernible with an empirically identifiable knowledge threshold.”

The study has resonance that even its authors may not fully appreciate. They frame their discussion proceeding from the assumption that “background knowledge is critical in many models of reading.” This is their own bit of assumed knowledge, which may or may not be true among teachers. Elementary education still worships disproportionately at the altar of reading comprehension “skills and strategies,” which insist on a content-agnostic view of texts (the same is largely true of state reading tests). Among the most common strategies is to remind students to “activate your prior knowledge,” connecting new and unfamiliar information to what you already know. Works great when you have prior knowledge to activate.

The authors conclude that their findings “suggest this approach would be useful for helping identify who may have difficulty understanding a text on a particular topic.” I had a slightly different takeaway. If we follow the “knowledge threshold” idea where it leads, Job One for elementary and middle schools would be to help students build a robust store of prior knowledge to activate. If we know there is a critical mass of background knowledge that means the difference between comprehension and non-comprehension, there can be no more valuable use of school time than getting children on the good side of the knowledge threshold on as many subjects as possible.

SOURCE: Tenaha O’Reilly, Zuowei Wang, and John Sabatini, “How Much Knowledge Is Too Little? When a Lack of Knowledge Becomes a Barrier to Comprehension,” Psychological Science (July 2019).