There's an Idea! (1978)

Vlad (Dimitry Shevelyov) is an outsider, laughed at by some of his classmates. His sister, meanwhile, sticks up for him, trying to tell the class his ideas. Vlad, you see, is a talented engineer, at the tender age of about 12 years, but he can't persuade people to listen to him, and accept that his civil engineering ideas are valid. In his mind, he sees himself as a young Leonardo Da Vinci, and puts himself in Da Vinci's place.