One reason so many diagnoses are missed is that thousands of schools in the U.S. continue to use an iteration of the discrepancy model to test children for learning disabilities. Moreover, for a multitude of reasons, including biases in IQ tests, a disproportionate number of those diagnosed—and helped—have been white and middle- to upper-class.

“It’s unfair, it’s discriminatory, and it disadvantages already economically disadvantaged kids,” said Jack Fletcher, co-founder of the Texas Center for Learning Disabilities in Houston and one of the first scientists to question the discrepancy model’s validity.

The model has shaped decades of policy regarding whose literacy is considered vital and worthy of extra help and investment—and whose is not. It is rooted in long-standing misconceptions about dyslexia. Reforming how the condition is defined and diagnosed could help many more children learn to read.

Speaking comes naturally to most children, being a gift of human evolution, but reading and writing are inventions that must be consciously and painstakingly learned. No one is born with neural circuits for connecting the sounds of speech to squiggles on paper. Instead, when someone learns to read, their brain improvises, splicing and joining sections of preexisting circuits for processing vision and speech to form a new “reading circuit.” To read the (written) word “dog,” for example, a typical brain will disaggregate the word into its constituent letters, “d,” “o” and “g,” and then summon from memory the sound fragments, or phonemes, associated with each letter. It aggregates these phonemes into the sound “dog” and retrieves the meaning of the word that matches that sound. Most brains eventually learn to do all these steps so fast that the action seems automatic. Some written words become so familiar that the speech circuit eventually gets bypassed, so that there is a direct association between the word as seen on paper or on a screen and its meaning.

Because human brains are organized in diverse ways, some people’s reading circuits end up being inefficient. Dyslexia is the most common reading disability. People with the condition, which is partly linked to genetics, often have less gray matter and brain activity in the parietotemporal region of the brain’s left hemisphere, associated with connecting the sounds of speech to the shapes of printed text.

Read the full article about diagnosing learning disabilities by Sarah Carr at The Hechinger Report .