We also had the same problem years ago with our one son, with the exception of it being a different medication. What we found out is that some pharmacies will mix the medication and put it in a liquid form and the child can even pick the flavor that they want. It's a little more expensive but definetely worth not having to struggle with this on a daily basis.
I'm not sure on your medication if this can be done, but I would highly recommend checking into it and see if its possible.
my son also was on concerta and i would give him a spoonful of peanutbutter (which he loves) and hide the pill in it...it slides down wonderfully!!! :)
Get some tictacs or other small candies and his favorite drink and let him have some short practice sessions. He may be picking up on your tension about the situation so try to make it fun so he'll relax about it. Do it with him (it'll be good practice for you too!) & have a contest or make funny faces or anything else you can think of to make it less stressful. And you could try setting up some kind of reward for when he does swallow the medication.
From a child's perspective, Concerta (even the 18 mg dose) caplets are fairly large and, of course, can't be chewed because the caplet must stay intact for the medicine to be released over the 12-hour span. They also cannot be crushed and sprinkled in foods such as applesauce or yogurt. Sometimes it does help to try to swallow it in a spoonful of one of these foods. If you are not successful over time, switching to a medication such as Metadate CD (which is in capsule form and can be sprinkled) can be helpful.