I think I was in second grade when I learned this. I was definitely in elementary school. This is not even eighth-grade grammar.
A period ends a sentence that is a statement (a telling sentence).
- I am going shopping.
- Sally likes Italian food.
- The sky is blue.
A question mark ends a sentence that is a question (an asking sentence).
- Are you going shopping?
- What kind of food does Sally like?
- What color is the sky?
This week I witnessed an executive and a teacher confuse the two. I wept.