I have every sympathy with parents of teenagers struggling to revise maths GCSE, I feel your pain…
So, I thought you might be interested something I have found helpful, Corbett maths cards. These cards are great, there is 1 card per topic and on the back, there are 3 Q codes taking you to a short video summarising the topic, one for past exam questions on the topic and one for the answers! Therefore, parents can support their teenagers without understanding anything about maths.
My daughter has been going through these cards, each topic takes from 15 to 45 minutes depending on how difficult the topic is. Working through these cards is a great way build confidence in maths and I would definitely recommend them. I only wish there were similar cards for science etc.
To get hold of the cards go to: https://corbettmaths.com/revision-cards/