Peter is a teacher and wants to teach his kids how to do green screen keying like they do with the weather on the news. Leo suggests Telescreen Wirecast as a budget solution. It costs about $400-500. Leo also recommends hardware solutions like the TriCaster 40, but it's expensive at $5,000. There's also the Blackmagic ATAM.
Then he would need the proper chromakey green. Painting the wall is a good idea, but there's portable stretch options as well. He'll also want to light it properly to make sure there's no shadows.