While I have not personal experience with the American education system, I can really see both sides of this ...
A couple years back someone very close to me was working at a small publishing house producing text books for elementary schools and I got to know a large portion of their staff fairly well. In a large part because they were staffed by humanities majors (which tend to be far more "progressive" than most university students) the staff was far more "progressive" than the population in general. You could see their political bias being represented in the books they were creating based on the topics they choose to emphasise, the historical figures they featured, the events they deemed significant, and the way they covered all of it.
This is not that uncommon, and this political slant can be viewed in textbooks for all levels of education from elementary school through University; and in University one of my professors insisted upon using a textbook that was 30 years out of print because of what he called the "Politicalization" of Canadian history.
Now, if the Texas Board of Education is trying to counter some of this bias by returning some focus and attention to important events that have been minimized, and a de-emphasis on lesser issues that have been pushed, then this could be considered a return to balance in the study of history. On the other hand this could easily go too far, and the pendulum could swing to the other extreme.
