I have been there! My son started having meltdowns and outbursts Kindergarten. The teacher was really fantastic and helped him through the year by giving special jobs (taking stuff to the office/other teachers and whatnot), reading to other kids, and giving him 1st grade worksheets... same deal in 1st grade, though with less success. 2nd grade things devolved completely... he had an older teacher who was wanting to retire and had zero extra energy for my son. We were in full-on crisis mode before I finally accepted my son needed SERIOUS help.
We did end up doing medication for his mood and his impulsiveness, and we got him evaluated by a neuropsychologist. This summer we got him in to a great cognitive behavior therapist, and then when school started he began doing group therapy with the cog. behavior therapist. He's been doing a MILLION times better in school this year.
I would strongly recommend they get him evaluated by a neuropsychologist or a developmental pediatrician. They are really the only doctors who are going to be able to do the full amount of testing/assessment, plus they will provide a full report and recommendations for what the school can do to help the kiddo.
Good luck to them. I wish I could give them a giant hug through the internet. Where they are SUCKS. They have to give in and accept the help of medical professionals... the sooner they realize that the sooner things will get better!