They already learned that slavery played a central role. They new changes are going to have it listed as the only cause, rather than one of three causes.
Slavery was the first order cause, so it would be correct to present slavery as having a central role.
source: Texas Declaration of Secession: http://www.civil-war.net/pages/texas_declaration.asp
"maintaining and protecting the institution known as negro slavery - the servitude of the African to the white race within her limits"
As opposed to most wars, where history was written by the victors, in the US Civil War was mostly written about by the losers. They immediately went about reinventing the war in order to ease their conscience. I mean, the South deliberate started the war to defend an absolutely evil act (slavery), and in the ensuing conflict brought utter ruin on their society. The North was complicit in this rewriting because their main interest was in reintegration and reunification of the country.
Unfortunately, fast forward 100+ years, and now we have people talking about state's rights, and not about slavery. Counterrevisionism, in this case, is more than justified.
As far as Southern states were concerned, slavery was perfectly legal, culturally acceptable and morally correct, so they wouldn't see a need to mince words. It's only in the modern context of historical revisionism that such whitewashing is necessary.
"The state's previous social studies standards listed three causes for the Civil War: sectionalism, states' rights and slavery, in that order."
I have emphasized the part that shows how, while that position avoids being formally completely wrong, it fundamentally misrepresents the situation. The reality is that the only significant issues (significant enough to lead to secession), with regard to the first two causes stated here, were over slavery. We don't have to guess about motives here, because the leaders were not shy about stating clearly, on the record, what their issues were.