Subject: What was the most important historical event in the advancement of space?

I am a second grade teacher in a county school writing a new curriculum.
Children often understand the basic of space but do not understand the 
why's and how's. In order to understand where the space program is today, 
one must understand where we have been. Many people disagree with the most 
important event and I would like to have another qualified viewpoint.

Re: What was the most important historical event in the advancement of space?