I am the greatest teacher out of them all, but alas in the end I kill my pupils.

Answer: Time

More Difficult Riddles with answers

More Difficult Riddles

I am the outstretched fingers that seize and hold the wind. Wisdom flows from me in other hands. Upon me are sweet dreams, my merest touch brings laughter
I am whole but incomplete. I have no eyes, yet I see. You can see, and see right through me. My largest part is one fourth of what I once was.
I bind it and it walks. I loose it and it stops.
I can be quick and then I'm deadly, I am a rock, shell and bone medley. If I was made into a man, I'd make people dream, I gather in my millions By ocean, sea and stream.
I can be short and sometimes hot. When displayed, I rarely impress.
I can be written, I can be spoken, I can be exposed, I can be broken.
I can move even when you are still. I can be one or many.
I can ruin your day, or darken your life. And while I'm expected, I'm never alright. I'm bad for business, and worse for your hair. Wherever I am, there's something not there.
I can travel from there to here by disappearing, and here to there by reappearing.
I climb higher when hot, But beware my rage, I’ll kill with a breath, If I can escape my cage
I count time, but have no end. Tick tick, but I am not a clock. What am I?
I don't have eyes, but once I did see. Once I had thoughts, but now I'm white and empty.