This can be due to several reasons:
- The child has a low IQ. This you can tell if the child takes hours to understand the concepts and cannot retain the concepts for long. There is no treatment to increase the IQ as it is a birth defect. But you can train your child to lead a normal life with the help of professionals.
- The child has dyslexia. This you can tell when even though the child understands the concepts, retains the concepts, but still cannot score well. The child might not be scoring well but will be good at something else. Dyslexia can be treated with proper intervention and therapies.
- There is something which is bothering your child. This can be confirmed if the child along with poor grades is not sleeping well, not eating well, shows other behavioural problems. Here, depression or anxiety can be the underlying causes.
In any case, it is best to consult a clinical psychologist or a psychiatrist for proper evaluation.