Is it illegal for a mother to beat there son with a belt?

I'm 14 with bad grades. I am doing my best to get them up, but my mother expects the impossible out of me. Earlier today she threatened to beat me with her leather belt. (And starve me.) When she spanks me or my sister, it's always on the behind, and usually 10-15 times. The last time she spanked me was when I was 12 with a spatula. I'm not gonna let her beat me when it's against the law, so I would really appreciate it if you told me if it's illegal or not. Thank you.