the basis for abnormalities at a cognitive level that are associated with the behavioral signs
of the disorder. The biological origin includes an interaction of geneti c, epigenetic, and en-
vironmental factors, which affect the brain’s ab ility to perceive or process verbal or non-
verbal information efficiently and accurately.
One essential feature of specific learning diso rder is persistent diff iculties learning key-
stone academic skills (Criterion A), with onset duri ng the years of formal schooling (i.e., the de-
velopmental period). Key academic skills incl ude reading of single words accurately and
fluently, reading comprehension,  written expression and spelling, arithmetic calculation, and
mathematical reasoning (solving mathematical problems). In contrast to talking or walking,
which are acquired developmenta l milestones that emerge wi th brain maturation, academic
skills (e.g., reading, spelling, writing, mathematic s) have to be taught and learned explicitly.
Specific learning disorder disrupts the normal pa ttern of learning academ ic skills; it is not sim-
ply a consequence of lack of o pportunity of learning or inadeq uate instruction. Difficulties
mastering these key academic skills may also impe de learning in other academic subjects (e.g.,
history, science, social studies) , but those problems are attributable to difficulties learning the
underlying academic skills. Difficulties learning  to map letters with the sounds of one’s lan-
guage—to read printed words (often called dyslexia)—is one of the most common manifesta-
tions of specific learning disord er. The learning difficulties manifest as a range of observable,
descriptive behaviors or symptoms (as listed in Criteria A1–A6). These clinical symptoms may
be observed, probed by means of the clinical interview, or ascert ained from school reports, rat-