im also a single mum with a 11 year old and a 14 year old,
its not easy enforcing rules on children who wont listen,
all i can say is i use removel of best liked items for a 24 hour period, like no pc, tv, toy and so on,
i have found parent line very helpful for advice and support,

maybe your mum could try talking to him and asking him what could he suggest to make things run better in the home, what does he think should happen when he plays your mum up, is there any family who can care for him part of the week while your mum works,
i tried this with my two and was suprized at how many good ideas they had about rules and punishments,
its finding a balance that suits both of them.

also what about the boys father? is he involved can he back your mum up? or stay with him part of the school holidays.

failing all that your mum could talk to her gp about his behaviour maybe counciling would help him and your mum.
good luck
x debs x

I have an eleven year old who winds me up too and although I am not single now I used to be,so know how it feels.When you have a partner it is far easier to switch off and wind down,enaberling you to switch channel so to speak.

It may be good for her to put some time aside to give him some undisturbed attention as sometimes bad behaviour is a way of seeking out attention.A firm,consistant approach where boundaries are set and not changed helps too.She should tell him quietly but firmly that swearing is bad behaviour and that it would make her happy if he did not do it.Try not to shout as it will go over his head.I know only to well how hard it is not to shout but it will keep everyone calm if you do not.

Hope this helps.