above (one's) head
Being too advanced or difficult for one to be able to comprehend, understand, or complete; beyond one's abilities. I thought I could handle this advanced math class, but the stuff we're learning is just way above my head.
above (someone's) head
Not understood by one because it is too complex or subtle for their comprehension. My jokes always seem to go above Stephanie's head, so I'm glad you think I'm funny at least.