All of the following three features are required for a person to have “learning disabilities”:

• global intellectual impairment (intelligence quotient less than 70),
• needing support/help to fulfil ordinary daily activities,
• onset during the developmental period (i.e. before becoming an adult).

An adult with mild learning disabilities has a mental age of around 9-12 years, but of course continues to learn throughout life and has adult biological motivations and drives. People with learning disabilities take much longer to learn and retain new information and skills compared with ordinary people.

There are lots of other conditions that can slow learning but which are NOT considered to be “learning disabilities” if the person does not also have global intellectual impairment, e.g.

• blind,
• deaf,
• severe epilepsy,
• dyslexia,
• autism.

There are many causes of learning disabilities, and for many people with learning disabilities the cause is never known. Some people are recognised as having learning disabilities at or before birth e.g. people with Down syndrome, whereas others are recognised during early childhood when they fail to meet developmental milestones, or struggle with school work. Some children acquire learning disabilities in childhood after illness, e.g. meningitis/encephalitis, or brain tumours. The age “cut-off” in the definition of learning disabilities is because having learning disabilities impacts on childhood development as well as being a long-term condition. Conversely, people who have illnesses in adult life resulting in impaired intelligence (e.g. head injury, encephalitis, stroke, or Alzheimer disease) will have had a normal development and skill acquisition during childhood; these people are therefore considered to have a dementia, not learning disabilities.

The terminology that is in use in the UK can be confusing, as different people use terms in different ways. The terms learning disabilities, learning disability, learning difficulties, learning difficulty, intellectual disabilities, developmental disorder, developmental delay, additional support needs, special educational needs, and special needs are all sometimes used to mean learning disabilities in the UK. The confusion is because these terms are also sometimes used to mean other things e.g.

• specific learning disabilities means conditions like dyslexia or dyscalculia,
• learning difficulties is also sometimes used to mean dyslexia or dyscalculia,
• developmental disorder is also used as a broader term encompassing learning disabilities, autism, language disorders, ADHD, motor disorders, severe epilepsy,
• additional support needs is a term used in education to cover a very broad range of conditions including learning disabilities, but also e.g. dyslexia, autism, blind, deaf, gifted children, bereaved children, English as a second language (education services aim that the right support should be available so that every child can reach their full potential, hence the inclusion of gifted children),
• special educational needs is a term used similarly to additional support needs.

In the USA, the term “intellectual disabilities” is synonymous with the UK term learning disabilities, whilst in the USA “learning disabilities” means dyslexia or dyscalculia.

People with learning disabilities often have other conditions as well. About 25% of people with learning disabilities also have autism. However, the majority of people with autism do NOT have learning disabilities in the way that the Baily Thomas Charitable Fund uses this term. Asperger syndrome is a type of autism, but people with learning disabilities never have Asperger syndrome, as its definition excludes people with learning disabilities.