I also have a son who is 11 and in the 6th grade.  I wonder the same thing.  He has been taking concerta since the second grade.  Recently I noticed excessive blinking in him.  I became worried as it seemed to get worse.  He would say he couldn't control it and it was messing him up in school.  He would lose his place while reading and even bump into things.  I contacted his doctor who told me to stop the concerta.  She said that a colleague of hers told her that in some children, after being on concerta usually between 2 to 3 years, will begin to have Tourette like symptoms.  So it has been 8 days now and occaisionally he will begin blinking.  I'm not sure what to try next.  His teachers were patient last week:)  He's forgotten home work assignments and struggles to complete simple tasks.  But he's gained 5 lb, doesn't look anorexic, and actually has a personality.