How can children be taught to respect their elders and teachers?

Through the parents' own example and by teaching specific manners, because the Prophet ﷺ made respect for elders part of the identity of his community.
He said: he is not one of us who does not show mercy to the young and respect to the old (Jamiʿ at-Tirmidhi 1919). Manners that can be taught from early on: giving the salam and shaking hands, speaking in a low voice, not interrupting, letting elders sit and eat first, and saying thank you. Children learn most from how their parents speak about grandparents and teachers at home. If parents criticise a teacher in front of the child, the child's respect for teachers erodes too; take the issue directly to the school. Respect also does not mean a child must obey an adult who tells them to do wrong or touches them inappropriately. See Educating the family.