The link between ADHD and anxiety is well known. Research estimates that anywhere from 25 to 50 percent of people with ADHD also have a co-occuring anxiety disorder.
Attention Deficit Hyperactivity Disorder symptoms include inattention (difficulty concentrating, organizing, and completing tasks), hyperactivity, and lack of impulse control (impulsivity).
Anxiety Disorders are diagnosed by chronic feelings of worry or nervousness, panic attacks, avoidance of fearful situations, social anxiety, obsessive-compulsive disorder, insomnia caused by worry, etc.
To diagnose either condition, symptoms must be chronic and inhibit normal daily functioning. For example, everyone feels temporary anxiety, such as when taking an important exam, but for someone suffering from clinical anxiety, symptoms do not subside, and often become worse over time.
While both ADHD and anxiety are linked, and can present similarly, they are clinically distinct. For example, a person with ADHD may experience anxiety about not being able to complete school or work assignments, but that does not necessarily indicate an anxiety disorder. Similarly, a person suffering from an Anxiety Disorder may not be able to concentrate well, but that does not necessarily indicate ADHD.
Parents and caregivers can often make helpful behavioral observations when talking to a mental health provider, and should be on the lookout for common signs.
For example, while a child that has trouble concentrating can become anxious, a child with ADHD will have trouble concentrating almost all of the time.
Similarly, avoidance of fearful situations is a common sign of anxiety. For children, complaining of a stomach ache or other somatic symptoms in the morning is a sign that they may be experiencing anxiety about attending school.
Keep in mind that none of this is a substitute for a comprehensive clinical evaluation. If you suspect your chid is suffering from ADHD or anxiety, consult your local mental heath professional. It is important to be properly screened by a mental health provider in order to receive proper treatment.
One thing to be aware of is that since ADHD is most often treated with stimulant medications (Ritalin, Adderall, etc.) they may exacerbate symptoms of anxiety.
If the anxiety symptoms become too uncomfortable, dosages and treatment plans may need to be adjusted. For example, some people choose to treat one condition with medication and the other condition behaviorally via therapy.
I find that a combination of treatments typically works best, but often there is a period of trial and error to determine which treatments are most effective for each individual.