The document defines learning disabilities according to IDEA as disorders involving one or more basic psychological processes related to understanding or using language, reading, writing, listening, speaking, reasoning mathematically or doing mathematical calculations. It notes that learning disabilities can be caused by conditions such as brain injury, minimal brain dysfunction, dyslexia or developmental aphasia. The prevalence of learning disabilities has increased exponentially over the past 20 years, with half of all special education services going to support reading difficulties. Characteristics can include average to above average IQ but inconsistent skills, difficulty with reading/writing, and slower work. Areas of specific learning disabilities include oral expression, reading, writing, math calculation and reasoning.