This was a book I read a few years ago as an eighth grader. I remember the book being fairly old, maybe written in the 80's?
It was a book about humans who were very advanced and went undercover to help another planet thrive. The humans taught a girl on the primitive planet telekinesis and gave them challenges to survive through.
The opening scene was the spaceship leaving I think? It had imperial in the title I believe. I don't know why I remember this but there was a scene where the humans give the girl a lantern and she asks them how they put the sun in a glass jar.