Was your American ancestor literate?

We might wonder if some of the ancestors way back in the 1600's and 1700's were literate or not. You might notice that family history researchers sometimes draw the conclusion that the ancestor was not literate, and will add the note "made his mark" or "made her mark." This is in reference to signing a legal document, such as a will or a  a deed with a stamp or the facsimile of a stamp. It was commonly done, and only sometimes for the reason that the signer was illiterate. The signer often was literate, and we may be fortunate enough to find that other documents have been signed with a personal signature, or that a letter or document has been written in longhand. There are a number of reasons that the person might use a stamp rather than a signature, including blindness or near-blindness, which may be a condition acquired in old age, or, along the same lines, feebleness due to illness, or it could be simply that a stamp was used just a matter of practicality and efficiency.
In the 1800's the same caveats apply--don't assume that someone was illiterate based on a stamp on a document. In many of the census records there is a note for each adult as to whether they could read or write. These notations are worth  looking for. Sometimes the designation is for reading, sometimes for writing, and sometimes for both, depending both on the census year and place. Again, finding letters, signatures or Bible entries of family births helps to indicate literacy. Someone had to make those entries.
In my own research of the Moraga family of California, who descend from Joaquin Moraga who was second in command in the De Anza expedition, I found a great deal of evidence in the census designations, letters, and in occupations (including teacher) to disprove the common notion that the family was for the most part illiterate.
This is not to say that many of our ancestors may have been illiterate. Certainly many of them were. But it is best to look at as much evidence as possible for each individual before just assuming that they could not read and write.