ADHD is different to a learning disability, although it is a cause of learning problems in children simply because the symptoms and behaviors of it result in the student not being able to concentrate for any significant length of time.
"ADHD is a neurologically-based disorder caused by a deficiency of a specific neurotransmitter (norepinephrine and/or its precursors, dopa and dopamine) in a specific set of brain circuits. Depending on which areas of these circuits are involved, the individual might be hyperactive, distractive, or impulsive.
Hyperactivity might involve up and down, fidgety, squirmy, wiggly behavior or might show only as fidgety hand movements. The distractibility might be to sound inputs, visual inputs, and/or to internal thoughts. Impulsivity might involve speaking before thinking, thus interrupting or calling out or might involve acting before thinking." Dr Larry Silver, MD, LDonline.com
It's important to know that ADHD is the term used for ADD and ADHD - they are the same thing. ADHD is the term doctors use to diagnose this condition. (source: www.add.org)
Diagnosing ADHD can be tricky because the behaviors of hyperactivity, impulsivity and inattention are also symptoms of anxiety and depression. Physicians diagnosing ADHD will look at the pattern of clinical history to help determine whether ADHD is present. If the behaviors are present only in certain settings or they occurred at a specific time, then anxiety and depression are the likely cause. If the behaviors have been there since birth and they occur in all settings, a diagnosis of ADHD can be established.
Treatment for ADHD involves raising the level of the deficient neurotransmitter by using medications such as Ritalin, dextroampetamine, Adderall or decreasing the breakdown of the this transmitter so that it stays around in the brain for a longer time. Different medications such as imipramine, desipramine, nortriptyline will accomplish this.
There are many practical things that teachers can do to help students with ADHD concentrate and focus in the classroom. Here we've linked to some articles that you might find helpful.
Classroom Success for the LD and ADHD Child by Suzanne H Stevens shows how some simple adjustments can be in the classroom can lead to success for the child with ADHD.
Checklists for Teachers by Sandra Rief provides lots of practical tips on getting, focusing and maintaining students attention - her best advice is to lighten up and have a little fun!