Approximately 5% of all public school students are identified as having a learning disability (LD). LD is not a single disorder, but includes disabilities in any of seven areas related to reading, language, and mathematics. These separate types of learning disabilities frequently co-occur with one another and with social skill deficits and emotional or behavioral disorders. Most of the available information concerning learning disabilities relates to reading disabilities, and the majority of children with learning disabilities have their primary deficits in basic reading skills. An important part of the definition of LD is its exclusions: learning disabilities cannot be attributed primarily to mental retardation, emotional disturbance, cultural difference, or disadvantage. Thus, the concept of LD focuses on the notion of a discrepancy between a child's academic achievement and his or her apparent capacity to learn. Recent research indicates, however, that disability in basic reading skills is primarily caused by deficits in phonological awareness, which is independent of any achievement-capacity discrepancy. Deficits in phonological awareness can be identified in late kindergarten and first grade using inexpensive, straightforward testing protocol. Interventions have varying effectiveness, depending largely on the severity of the individual child's disability. The prevalence of learning disability identification has increased dramatically in the past 20 years. The "real" prevalence of LD is subject to much dispute because of the lack of an agreed-upon definition of LD with objective identification criteria. Some researchers have argued that the currently recognized 5% prevalence rate is inflated; others argue that LD is still underidentified. In fact, it appears that there are both sound and unsound reasons for the increase in identification rates. Sound reasons for the increase include better research, a broader definition of disability in reading, focusing on phonological awareness, and greater identification of girls with learning disabilities. Unsound reasons for the increase include broad and vague definitions of learning disability, financial incentives to identify students for special education, and inadequate preparation of teachers by colleges of education, leading to overreferral of students with any type of special need. There is no clear demarcation between students with normal reading abilities and those with mild reading disability. The majority of children with reading disabilities have relatively mild reading disabilities, with a smaller number having extreme reading disabilities. The longer children with disability in basic reading skills, at any level of severity, go without identification and intervention, the more difficult the task of remediation and the lower the rate of success. Children with extreme deficits in basic reading skills are much more difficult to remediate than children with mild or moderate deficits. It is unclear whether children in the most severe range can achieve age- and grade-approximate reading skills, even with normal intelligence and with intense, informed intervention provided over a protracted period of time. Children with severe learning disabilities are likely to manifest an increased number of and increased severity of social and behavioral deficits. When children with disabilities in reading also manifest attention deficit disorder, their reading deficits are typically exacerbated, more severe, and more resistant to intervention. While severe reading disorders are clearly a major concern, even mild deficits in reading skills are likely to portend significant difficulties in academic learning. These deficits, too, are worthy of early identification and intervention. Even children with relatively subtle linguistic and reading deficits require the expertise of a teacher who is well trained and informed about the relationships between language development and reading development.