The maids of the 30s, 40s, and even 50s in the South were often like surrogate parents.  This role, a carry-over of the mammy from the Old South, was not uncommon in many households of the South.  In fact, in their care for the children, many of the maids took a more active part in the discipline of the children than did the parents, especially the father.  Calpurnia is representative of this typical maid; she is "old school," as they say in the South.  For, her discipline involves physical action as well as chastisement; it is quick and to the point.  For instance, when Jem and Scout sneak back to the courtroom in defiance of Atticus, she appears with little regard to the proceedings of the trial, "making her way up the middle aisle, walking straight toward Atticus."  Atticus must stop and ask the judge for permission to attend to the children.  When they ask Atticus if they may return since they have already heard most of the trial, they can tell "Atticus was relenting."  This would not happen with Calpurnia.

While there are certain behaviors that neither will permit, the reasoning that Calpurnia uses with the children is more concrete and practical.  For example, when she scolds Scout for criticizing Walter Cunningham's manners, she tells her cryptically that Walter is "company," and she should not be impolite, removing her physically from Walter to equally embarrass her and give her a punishment.  Atticus, however, would correct her, but he would probably have her apologize at the table to Walter.  Later, as he does in the novel, he would spend time reasoning with Scout, explaining that one needs to understand others less fortunate and "consider things from his point of view." 

Both people of integrity, Calpurnia and Atticus differ mainly in their perspectives. While Calpurnia is less educated, she perceives situations in their simpler, more immediate forms; on the other hand Atticus--who is, nevertheless, always  supportive and respectful of Calpurnia--is ever the rational, erudite man, who teaches his children to consider circumstances and reasons beyond the immediate situation.  Together, they make a great team for rearing bright, strong-willed children like Jem and Scout.

In my opinion, Atticus and Calpurnia are very similar individuals on the inside, with very different exteriors.

Both have strong moral values for the children and work to hold them accountable for their actions. The way they approach that might be different. For example, when Walter Cummingham pours syrup all over his ham, Calpurnia takes Scout and removes her from the situation and maker her eat in the kitchen. Cal's point is to teach Scout to treat company with respect, no matter how odd their tastes might appear. This humiliated and irritated Scout during an already tough day. Cal reigned her moral teaching on Scout with great passion and fortitude.

Atticus on the other hand, when he gets angered with the children says rather matter of factly, to stop what they are doing. His dry demeanor almost makes you wonder if he has emotion at all, but he always knows what they are doing, and he steps in to correct only with firm words and examples in action.

Both moral characters model how race should be dealt with to their peers in their own race. Calpurnia loved Scout and Jem as if they were her own children. Atticus fought for Tom with passion and against the will of the white folk.