To be honest Jamie, I can't put a factual time on it. If I remember right, things started to go 'South' (in the circular file) around the early 1970's. A lot of those books were out of print and they just quietly phased them out of circulation. Our librarian is from Texas. She keeps as many as she can get her hands on. Even though we are a public school, a large number of our students are military brats. As a whole, I've found them to be less judgemental and when talking to them on a history lesson, they ask some really interesting questions. They hold discussions and I had one kid who was being a bit goofy (ADD and he just was bored) and the others told him to be quiet, they wanted to hear the story. That was refreshing to say the least.
After the big Civil Rights activities in the late 60's is when the 'systems' started to 'broaden' the students knowledge. Once MLK got a whole day in his name and then there came Black History Month, any real large scale chance of telling our version of history was over. Not only do they have a month, plus a day, almost every 3rd lesson in the readers, the writing workbooks and any other lesson has either a Black or Hispanic theme. Mostly Black. I'm so tired of Harriet Tubmann's story. Some times if I'm in a class when they're reading it I sort of add to their knowledge base by informing them that she would shoot to kill any of those she was aiding and abetting if they thought about turning back. Gotta get the whole story in those lessons ya know.
On the good news side of the coin. The last round of textbook scanning and rewriting to suit those on the committee in Texas (yes, they do seem to make the decision for the rest of us) was real nasty. They disallowed Jeff Davis letter for the reason the states wished to seperate because it did not say "keeping the institution of slavery" was a reason. I guess if it doesn't fit the committee's version, it's dumped. Anyhow, I have seen more in recent years on the South in a much kinder light. Some textbooks even explain that slavery was allowed when the first settlers showed up on the shores. They do give the South some names to remember like Lee, Jackson and Davis. Those used to show up looking like wanted posters.
I also saw in a 5th grade text that they explained that slavery was still legal after the EP!!! Soo, maybe there's hope yet. There are also individual teachers who spend a goodly amount of time on that era and give a fair view of both sides. Many of them have some of those 'tossed' bio's in their personal collection for class reading in their rooms. I know one who works that time in history into his math lessons. He's an Alabama boy, bless his heart. :)