How did they deal with slavery and Columbus?
I attended both public and Catholic schools. There wasn't much difference in the teaching of slavery or Columbus. Slavery was taught as an historic evil. Columbus was sanitized in the both public and Catholic schools back then.
Certain historic events were taught in a vastly different manner in the Catholic schools between the time my parents went to school (pre-Vatican 2) and the time I did (post-Vatican 2). For example: when my mom was in Catholic school, the Mexican Revolution and Spanish Civil War were taught as primarily anti-clerical in nature with the underlying political and economic grievances as minor secondary points. The Catholic Church aligned with Franco in Spain and against Juarez in Mexico. The difference in the social teachings of the Church between pre-Vatican 2 and post-Vatican 2 cannot be over-emphasized. To put the pre-Vatican 2 Catholic Church in perspective, Pope Benedict XVI, i.e. the Panzer Pope, was in the reformer camp during Vatican 2 deliberations.
As far as evolution goes, the Catholic Church views evolution as fact. It insists that at some undefined point in human evolution, the human form became a suitable vessel for an eternal soul and, through the grace of God, became fully human. The Church has taken no stance on exactly when this occurred and probably never will.
The biology of abortion was accurately taught in biology class. Because the Church's teaching on abortion was crystal clear, the biology teachers didn't have to tiptoe around it and could simply present facts of fetal development and where abortion fit in.