As much as I love history now, I found it a confused jumble when I was in school. I was able to memorize the dates and events (for whatever that was worth), but I could find no depth to anything I was taught: it had no meaning, no purpose, no clarity.
I spent decades digging through books and museums before I located the problem, which is this: The history you were taught in school wasn't exactly a lie, but it was selectively presented. Useful facts were presented to you and less useful facts were excluded.
The big question, of course, is this: Who decided what was "useful"?
In the case of schoolbooks, the answer to the "who decided" question is simple: The group that paid for the books.
As a result, textbooks present the history that makes government look good. The government pays for all those books, after all. And since private schools typically end up using the same books, their students are affected right along with the kids in government schools.