Originally Posted by
The Tatterdemalion King
Because the amount of other things you need to know to actually understand history, and think about it analytically, is rarely complete in high school. They also, probably, have electives available that cover whichever worlds (Federation or otherwise) and elements of society (economy, conceptions of justice, science, philosophy) which the student is interested in the history of.
The specific history of Starfleet and the Federation as a body (instead of the bodies that make up the Federation) and how they interact would be the key thing they would need to teach the students. Starfleet Officers require perspectives on how Starfleet actions have shaped history in the past (and depending on what era you're playing in, the future : P)