My son has ADHD and we started him on Adderall XR 10 mgs (which would be equal to 5 mgs of Focalin, when he was seven years old. As soon as the medicine was in his system (about 20 minutes) we could see a change in his behavior. He would calm down and be much more cooperative. Most of the teachers commented on the change within the first day or two at school. His grades went up to straight A's in the first six weeks and more unbelievable he went from many X's in conduct to straight checks. We switched him to Focalin XR 10 mgs when he was 12 years old. Again, the change was almost immediate. It is my understanding that with these types of medicine, the effect is obvious within 30 minutes and wears off after 6-8 hours. There is no long term effect. It only works while the medicine is in his system. This is true with all of the stimulants - Focalin, Adderall, Ritalin, Concerta, etc. If you are not seeing a noticable change the first few days, then he may need to try a higher dosage or a different medicine.
There are some other types of medications, like Strattera, that take a month or two to work. We also tried this when he was about 7 or 8, but it only seemed to make him drowsy and obstinate. We kept him on it for a month, then went back to Adderall.
Not every child reacts the same to each medication. Some kids do better on one kind than another. But you really should see a significant difference the very first week.