I'm afraid you misunderstand.
My question has nothing to do with high-school. I simply wanted to provide an educational baseline.
Now, please ask yourself. Do you know the Earth is round or do you believe it is round? Most people claim to "know" it when, in fact, they simply believe it.
And anyone can believe anything.
The only way to actually know something of this nature is to be in possession of a specific kind of methodology. In particular, scientific methodology.
Yes, it is possible to Google this matter... in general. However, is there a layman's experiment that demonstrates the Earth is round? In my opinion, this is a question relevant in this kind of forum.