Specialmoms comments are correct. I do get the feeling that since Concerta is a slightly newer drug (and longer lasting) that getting the dosage correct is a bit more trouble. Good article on this here - http://www.addadhdblog.com/concerta-getting-the-right-dose/#b6e48
Just keep in mind that all kids are different and react differently, so one person's experiences may not be the same as the next.
Please feel free to post if you have any more questions.
I am sure that Sandman will have some input to give you. The main difference I've read about extended release focalin verses extended release concerta is that focalin works faster (within 30 minutes of taking it) and is better for a child that needs the help prior to leaving for school and that type of thing. So, it is reported that it begins working fast in the morning and continues to control symptoms during the day and then tapers off at hours 10 to 12. Concerta may have a slightly better effect in those last two hours but less of an effect early on in the day after taking it. Both have a pretty similar side effect profile and you are familiar with these from your child's current medication. goodluck