"I don't think the teachers understand the consequences of having a mother who is ill. Mum might be upset when I get in after a hard day at school and I have to calm her down.
"I don't do my homework. I don't have the time, then it all piles up and I have to do it in a rush. They say 'you're not doing your best', but it is my best. I do try hard but nobody seems to realise what is going on at home."
Sarah is 15 years old and would love to study medicine at university one day. She thinks that is "probably out of the question now", because for the past two years - since Sarah has combined going to school with looking after her mentally ill mother - her school work has hit rock bottom.
Now a new report and guidance pack for teachers from the Children's Society has highlighted Sarah's plight and that of an estimated 51,000 children like her.
Jenny Frank, author of the pack, says: "These children frequently develop behavioural problems in school which can all too often lead to exclusion. Sadly, schools often don't know about the family situations until it's too late."
She cites the example of one boy who was so disruptive and loud in class that he was eventually excluded.
But when his home environment was investigated it was discovered that his father had left, and his mother had multiple sclerosis. He was responsible for caring for his mother almost alone.
The boy had to be so grown-up and serious at home that when he got to school he needed to let off steam.
Nobody at school realised what was going on because he never said anything and was never asked. Then when his mother missed appointments with the head to talk about his problems it was thought that she was an uncaring parent, because no one knew the real reason was that she was too ill to attend.
"I've known other children who appeared sullen and quiet. That can be equally misunderstood. As can lack of concentration - it may simply be that they are too busy thinking and worrying about the person at home," said Ms Frank.
Talking Together - a pack for use in schools with 11 to 16-year-olds is available from Resource Base on 01703 236806, price pound;7.50