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The origins of this idiom.
The meaning of this phrase.
Phrases and Idioms - The Meanings and History For Popular Idioms and Phrases | Use this handy list of phrases to search for more!
Thinking alike or understanding something in a similar way with others.
The origins of this phrase are unclear, however, one could guess it stems from schools, where teachers and students must be on identical pages in their books. Others have their own ideas as to its origins, but I don't think anyone really knows for sure.

Additionally, the expressions looks to be recent, as in, you might have been alive around the time it became commonly known and used.

I can only find it recorded as far back as 1974, used by the Corona Daily Independent on the topic of football:

"I think we can beat Washington and whichever team we play next to get into the Super Bowl. If 47
players and our coaches are all on the same page, we can do it."
* The rules will be changing around the office this upcoming Monday, so I wanted to be sure and tell everyone far enough in advance so that we can all be on the same page once they hit.
Note: The origins for most popular idioms are nearly impossible to find, if not completely! What's provided are the theories that may be plausible to how a phrase originated, but not necessarily so.

In addition, quotes that contain a phrase may be taken from old newspapers, poems, or books that were written centuries ago, but this by no means shows they originated from these. In all likelihood, if an expression is being used in a newspaper, it's probably already well known, and thus, from an older period of time.
Know Your Phrase - Common Idioms and Phrases, Their Meanings and Origins > O-Letter Sayings