If a child aged 10-12 is not declining words during conversation, they will likely have reading and writing difficulties. In such cases, significant work with a speech therapist is necessary, and it is recommended that parents also work with the child at home.
Remember, your child is not intentionally making mistakes; the teenager faces a problem that upsets them as much as it does you. Therefore, if the child struggles with reading or writing correctly, do not increase the volume and time of practice, as this usually leads to the opposite result – the child will simply become afraid to read or write, and these exercises will become their least favorite subject.
The more involvement and warmth you show the child while helping them overcome this problem, the faster they can cope with the difficulties.