I think the biggest problem, is that new things get added to history books every year, and that they cant go in to depth on everything because they need to teach it all by the end of the year/ semester, Im in U.S. History right now at OSU, and we have to cover from the revolution all the way modern history from August to December.
My AP U.S. History teacher in high school was the best history teacher I have ever had, I had him my freshman year in HS (Western Civilization) then again as a junior (U.S. History). For some of the things he just rambled on dates and names, for things like the industrial revolution, but he would go into depth on alot of stuff, since the book we had did not. When we got to WWI he let us "Play" WWI, he told us to put our desks up in rows on opposite side of the room, to signify the trenches and no mans land, then he told us to get paper and roll it into a ball, the we "fought" with the paper, it was fun. His dad was a member of the 101st Airborne in WWII and was with the Band of Brothers division (502nd PIR?) all the way to the Eagle's nest, so when we got to WWII he knew alot, but we just did not have enough time to go indepth on it before our AP test cause we had to study everything else. I discussed with him the Silent Service in WWII, and he let me do an extra credit Powerpoint on it, and he was really suprised on all the info, cause he had no idea.