whether or not Strattera works is not a matter of belief
Strattera is a selective norepinephrine (noradrenaline) re-uptake inhibitor. Norepinephrine is one of the neurotransmitter necessary to transport information between nerve cells in the brain. After it has been released from the nerve cell and "done its job" it is taken up again by the nerve cells. By inhibiting this process norepinephrine is available for a longer period of time.
Norepinephrine is associated with attention, while serotonine is associated with impulse and dopamine with drive. So it seems quite logical that Strattera could work well for ADD. (And I personally believe that this will probably apply in particular to the inattentive type).
Norepinephrine is also said to have an effect on the availability dopamine (the neurotransmitter Ritalin is mostly having an effect on). Thus an increased availability of norepinephrine should also increases the level of dopamine available.
Strattera does not work for everybody, nor does Ritalin or Concerta or Adderall or whatever. However, there have been studies with children and adults which have shown the effectiveness of Strattera. I have also read statements of people who are getting on well with Strattera (or their kids do).