Exercises for teaching GUI / Windows interaction basics
The last time I took a session on UI, that was when I was teaching these students who had finished a course on C sharp (dot net) and now wanted to build simple UI so they can turn their just learned programming skills into visibly usable software.

Since they were on dot net, I advised them to start by building a calculator using WPF. When I say calculator, it was a simple calculator. Build the number pad, and then implement just the addition and subtraction. While many of them were proficient in programming, they found themselves baffled...connecting the UI with code that would otherwise work just fine on the console. As they got the hang of things, I asked them to add more and more UI elements, until they had a full fledged scientific calculator with a fairly complicated UI. 

My advice to those who are new to UI is to allow the UI to evolve, and make sure that your backend development skills are up to the mark.