Why can ADHD make it difficult to finish schoolwork or other tasks?

Attention-deficit/hyperactivity disorder (ADHD) can make it difficult to finish schoolwork or other tasks due to persistent behavioral traits such as distractibility, forgetfulness, and difficulty sustaining attention. These challenges are not a result of deficient intelligence but rather stem from neurobiological differences that affect how the brain manages focus and impulse control.12

Research indicates that individuals with ADHD may have a reduced ability to resist focusing on extraneous stimuli, making it harder to maintain concentration on a single task. This is linked to developmental differences in the brain's "braking system"—specifically the cortical-striatal-thalamic-cortical circuit, which is responsible for impulse inhibition. Furthermore, dysfunctions in the brain's reward circuit, often involving the neurotransmitter dopamine, can alter behavior and motivation. Because this inhibitory circuit may experience a developmental lag, many individuals struggle to regulate these impulses until later in life, which directly impacts their ability to follow instructions and complete tasks in settings like school or work.231