What triggers the behavior something usually does, children hate that morning rush to get them out of the door it is worth getting up earliar so there isnt that stress before school. You say he gets angry over silly things ,what silly things? they may not be silly to him ,as he misses his Dad this could also be an upset to him, is it not possible for him to be connected to his Dad at all?
My son is 8, and he also does this. This morning he hated me and I was Stupid! Me and his father is divorced and I am married again. He is seeing a counceler for anger problems. Recently his counceler wrote 5 things that he needs to work on, and had him sign it (like a promise note) This seems to work, and I have it on the fridge, and remind him of his promise and that he agreed to it by signing it. We have a lot less outbursts since we did this! My son is also on medication for adhd! Hope your situation gets better!