I don't have any experience with Concerta specifically but I can give come general info.
Usually the doc will start on the smallest dose and try to work up to the max dose. So you may not see anything on this lower dose. Just because you're not seeing anything doesn't mean the medicine won't work. It may just need a higher dose.
Watch for "rebound". This is when the body is coming off of the medication. Sometimes the symptoms come back even worse. My son had emotional meltdowns when Adderall wore off but when he switched to Ritalin they went away. Rebound is NOT something that you have to put up with. Things can be adjusted (higher dose, doses given closer together, etc) so make sure to call the doc if you see it.
Also remember that a lot of kids metabolize these stimulants much faster than it says on the bottle. Like my son-he went through a six hour Adderall in 4 hours and he went through a 4 hour Ritalin in about 2 1/2. So just because the symptoms come back before the time's up doesn't mean the med isn't working.
Please check in here with any symptoms or side effects. One of us has probably experienced it! Good luck and I think you'll be pleasantly surprised! "Kudos" to you for getting your child the help he needs! 