7 year of son with Migraine's

I have a 7 year old son that starting having headaches around a year ago.  Beginning of the year I was told that they are migraines.  Since school has started (Aug) he is having them 4-5 days a week.  Just a month ago he was started on Depakote Sprinkles.  by increasing the dose he was up to 250mg 2 x day and has no improvement.  He is now at 250mg am and 375mg pm and I am not seeing no improvement.  Tonight was the first after he has gone to bed that he has been waken by a migraine.  Does anyone have information that Depakote Sprinkles really work for migraine's?  I don't want him on a medication that wont work for him but don't know what else to do.    He is finally getting an MRI on Nov 16th.  Hoping that everything comes out good but what am I going to do about the migraine's.

Thanks