I really really know where your coming from with your mum making excuses!
When my little brother first went to college, he chose the college he wanted, and spent the entire time playing on the computer and going to see friends, getting drunk, stoned. So he failed miserably in his AS levels (nothing over a E).
Short story hes at a new college and has done exactly the same thing. Mum says it because hes the only child in the house and she spoils him rotten, blaming a lot of our problems on my parents very messy divorce.
He can do no wrong as far as shes concerned which makes me really resent him to a massive extent, since i was the good child and always did my work, went to uni, did good, and wants to actually learn things as well as have a good social life!
But it would appear that time will actually heal the rift that is there. He should realise that he was a little $hit to the family.