Need advice on helping a child deal with bullying in school

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I recently noticed that my 11 year old cousin is constantly trying to avoid going to school. So I decided to ask him why, and he told me that he is the favorite target of bullies in his class, that he can't stand it any more. I tried to talking to his parents about this. But it seems that they are convinced that their son is just being lazy. So what can I do to make my cousin want to go back to school? And how do I explain to his parents that there is a more serious reason behind his behavior? I'd appreciate your advice on this. Thanks in advance!