There are two main groups of symptoms: inattentive; and hyperactive-impulsive. A child or adolescent with ADHD may show symptoms from predominantly one group or the other or combine symptoms from both groups.

Symptoms of inattentive include:

Not listening to what is being said.
Making careless mistakes in schoolwork or activities.
Frequently shifting from one activity to another.
Forgetfulness, losing items frequently.
Being messy and disorganised.
Avoids or dislikes tasks that require sustained mental effort.
Easily distracted by surroundings.

Symptoms of hyperactive-impulsive include:

Fidgeting or squirming.
Talking excessively.
Having difficulty remaining seated.
Frequently interrupting conversations or activities of others.
Blurting out answers before questions have been completed.
Having difficulty waiting for their turn in games or activities.
Having difficulty playing or engaging in leisure activities quietly.

It is worth noting when these behaviours:

Become severe and persistent over time.
Become pervasive and occur consistently all the time, whether it is at home or in school.
Impair their ability to make friends, get along with others or perform their tasks in such an instance, the child may be suffering from ADHD.