Answer:
I am of several different kinds, but the one you pick doesn't do its job. What am I?
Never ahead, ever behind, yet flying swiftly past, for a child, I last forever, for adults, I'm gone too fast.
I cover what's real; hide what is true, but sometimes bring out the courage in you. What am I?
I go from house to house a messenger small and tight. Whether it rains or snows I sleep outside at night.
I am used when you jump off a bridge for fun.
Written on with words of white, Has the color of the night, Is the teacher's best delight, And a student's daily fright