My baby was not able to sit and stand well when she was 6 months old, so we were asked to come back when she was 9 months old which was last month. She was tested again and everything was okay. She could sit and stand well while holding on the chair. She could also move the toy from one hand to another.
Anyway, when she was 6 months old, the nurse asked me to train her everyday how to sit and stand.