What is the ruling on the school refusing to allow students to sit on chairs and tables, claiming that sitting on the floor is from the Sunnah?

Sitting on the ground or on a chair is not a Sunnah or a bid‘ah (innovation) in itself; rather, it depends on the custom of the people and the place. In mosques, sitting on the ground is customary, and it is not permissible to sit on chairs except out of necessity, such as for a teacher, a khateeb (preacher), or for the sick. As for other gatherings, the matter depends on what people are accustomed to and what is most suitable for them. The Prophet, peace and blessings be upon him, and his Companions sat on chairs out of necessity, and there is no harm in eating at tables or using spoons and forks.