Every teacher of struggling readers has experienced the moment when a student says, “I read it, but I didn’t get it.” It can be a bewildering experience. Why don’t they get it?

For several decades, elementary schools in New York City and across the country have turned to Columbia University education professor and acclaimed reading guru Lucy Calkins to answer that question. But in recent years, her influential and best-selling “Units of Study” curriculum has faced an intense barrage of criticism from experts who complain its “balanced literacy” approach is ineffective and gives short shrift to phonics — teaching children to look at pictures and guess words, for example, instead of sounding them out.

Schools Chancellor David Banks has announced plans to move literacy instruction in New York City away from Calkins’ curriculum in favor of approaches based on the “science of reading,” including phonics. Perhaps as a result, Calkins now appears to have conceded the argument, promising in a lengthy New York Times article to include “daily structured phonics lessons” in her program. That’s welcome news, but it’s not enough.

The South Bronx elementary school where I taught 5th grade for several years was a proponent of Calkins’ approach. We adopted her teaching methods and employed her literacy coaches for years, to very little effect. Her greatest sin against literacy comes after kids learn to “decode” the written word, whether or not they are taught with phonics, which is just the starting line for reading.

Calkins’ literacy philosophy is aimed at children developing a “lifelong love of reading” and discovering the intoxicating power of their own voices as writers. This mostly entails kids reading books they chose themselves and writing about their own experiences and interests. That may sound engaging and fun for kids (and it often is), but it can be fatal to sophisticated adult literacy, particularly for disadvantaged children.

Here’s why: Reading feels like riding a bike to good readers. Once you learn how to pedal and balance, you can ride nearly any bike. Reading may feel the same way; reading comprehension, however, is far more complicated. It depends on the reader and writer having in common a lot of background knowledge, vocabulary and context. Consider the common word “shot.” Phonics instruction can ensure children can read the word, but it means different things on a basketball court, in a doctor’s office and when the repairman uses it to describe your dishwasher.

Words and the ability to “decode” them are just the tip of the iceberg; comprehension lies beneath. The critical role of shared knowledge to language proficiency is the basic insight of another, less-heralded professor, the University of Virginia’s E.D. Hirsch Jr. Hirsch is something of the anti-Calkins and preaches a very different message: For education to work as an engine of equity and upward mobility, schools must do all in their power to expand children’s horizons, ensuring they get a well-rounded education in science, history, literature and the arts — access to the rich knowledge and vocabulary that undergird literacy.

Calkins’ work mostly disregards this fundamental insight, focusing students’ attention in the mirror instead of out the window. For low-income kids who are less likely to grow up in language-rich homes and don’t have the same opportunities for enrichment as affluent kids, the opportunity costs of Calkins’ “philosophy” are incalculable. Endless hours of class time that could be building knowledge and vocabulary are squandered.

I witnessed this daily in my South Bronx elementary school, where fewer than 20% of students passed state reading tests. I never had a single student unable to read words printed on a page. When they were reading and writing about topics they knew — the Calkins method — students did well. But when asked to read about unfamiliar topics on state tests, they often struggled. They read it, but they didn’t get. One principal I worked under attributed our low scores to “test anxiety,” but that wasn’t the problem. Their education was all mirrors and no windows.

It is well that Calkins has finally seen the light on phonics, however begrudgingly. But her approach commits even greater sins, particularly against low-income children, that phonics alone can’t fix.

Robert Pondiscio is a senior fellow at the American Enterprise Institute.