When I was in school 25 years ago, I was taught to put two spaces after a full stop.
My elementary school daughter is now learning to type. In the textbook that she has, it says to put only one space after a full stop.
Has the standard changed?
Yes, it's a throw-back to the era of fixed width fonts. The details are explained in the Slate article linked above.
I was in school 20 years ago and I was on the tail end of the era when computers had green screens with fixed width fonts. Double-spaces were starting their slow decline with the advent of the original Apple Macintosh.