Gayle, is your grandson seeing a psychiatrist?  Has the teacher been able to give you any insight about class activities or incidents that have led to this behavior.  The other advice on this page, I think, is right -- you need to see a professional about medication options.  But the fact that your grandson has had similar behavioral outbursts on different medications and different dosage levels may indicate that he is facing some other challenges or symptoms that ADHD meds alone are not addressing.  One thing to consider is your grandson's age and whether or not he might be entering puberty or going through some changes not unlike puberty.  Boys who are undergoing rapid hormonal changes due to growth spurts or puberty sometimes have behavioral outbursts that may be impacted for better or for worse by certain medications.