In chapter 4 Dr. Ehrman claims that the Gospels are not written by eyewitnesses because the disciples of Jesus would have been illiterate.
"From the Gospels we learn that the disciples of Jesus, like him, were lower-class peasants from rural Galilee. ... We have some information about what it meant to be a lower-class peasant in rural areas of Palestine in the first century. One thing it meant is that you were almost certainly illiterate. Jesus himslef was highly exceptional, in that he could evidently read (Luke 4:16-20), but there is nothing to indicate that he could write. In antiquity these were two separate skills, and many people who could read were unable to write.Ehrman notes that even the Bible teaches that the apostles were illiterate and unable to write since Peter and John are described as being "unlettered" in Acts 4:13 by the Council of religious leaders using the Greek word agrammatos. He then states that they would have known Aramaic and not Greek. Thus concluding that the disciples were "[l]ower-class, illiterate, Aramaic speaking peasants from Galilee" who could not have written the Greek Gospels that we have today.
[the] upper class people who had the time and money to get an educations (and their slaves and servants taught to read for the benefit of such services to their masters). Everyone else worked from an early age and was unable to afford the time or expense of an education. "
Now Bart Ehrman knows a lot more than I do regarding ancient history, the Greek language, etc., however he does seem prone to taking facts and possibilities and accentuating them in the most negative light (see Daniel Wallace relating his debate experience with him regarding textual variants here and here). The claims he makes regarding the education and literacy of Peter and John based on Acts 4:13 are not accepted by others with expertise in the Greek language (see NET Bible translation notes for that verse). All good readers know that the context should dictate how a word should be interpreted. In this passage the Council which consisted of experts in the Scriptures (Acts 4:5) could have been amazed at the ability of fishermen to expound on the meaning of the Scriptures because they were untrained in such matters. This certainly fits with the overall passage and does not require Peter or John to be illiterate (unable to read/write). The Law was what the Council were experts in so they may have been amazed at how Peter & John could be so confident in what they were teaching. In fact this confidence may have been what reminded them of Jesus (Acts 4:13; Mark 1:22).
However even assuming that Dr. Ehrman's claims are correct, we can defend the Petrine writings. I am focusing on these writings since I have been studying the Gospel of Mark. The Gospel of Mark has a long history of being written by a man named Mark who worked with Peter and recorded his teachings. See prior blog entries on the Gospel of Mark for details. Mark himself was a cousin of Barnabus (Col 4:10) and part of the tribe of Levi (Acts 4:36). Barnabus having owned land (Acts 4:37) would have been educated and able to read and write using the criteria laid out in "Jesus Interrupted". It is therefore likely that Mark, his cousin could have these skills as well. Mark is noted as being with Peter in one of Peter's epistles (1 Peter 5:13) and if Peter could not write then it makes sense that he needed someone like Mark to travel with him. So the Gospel of Mark contains the recollections of Peter but were written down by Mark who could read/write and was a traveling companion of Peter.
The epistle known as 1 Peter is explicitly noted as being written by Silvanus (1 Peter 5:12) an amanuensis so we have no problem here. Silvanus would have recorded the thoughts of Peter.
The epistle known as 2 Peter is considered to be written in rough, unpolished Greek - see Wallace's article for details. This could allow for Peter having learned enough Greek to write it himself since no amanuenses is mentioned, though it still could have been written by an amanuenses without the attribution.
The main point is even if the apostles were unable to write this does not force us to reject the writings attributed to Peter (including the two epistles or the Gospel of Mark). These writings can contain the thoughts and recollections of Peter - an eyewitness of Jesus (Acts 4:13; Mark 1:16, 14:66) - that were physically written down by two other men - Silvanus and Mark.