I despair at my son and his lack of commitment to school

[Jerseyknit]

I feel like a failure when it comes to getting my son to work at school. Over the years I've paid for private tuition, I've supported his music lessons and always encouraged him to work hard. He is 13, has gcse's coming up and the school are offering him extra help but he just can't be arsed. I work full time, mostly at home but that's not always been the case. I've paid to have a friend's very capable older older brother to help him improve his work but he just doesn't want to put the work in. I'm really not sure what else I can do. If I ground him or take away his pocket money I don't think it will make much difference. Any strategies will be very gratefully received? Please (begging and pleading face and on my knees)