One of the assumptions of Form Criticism is that the disciples did not write anything down during Jesus’ lifetime or even in the earliest years of the church. The teaching and activities of Jesus were passed along as oral tradition through teaching and preaching. The more radical / early Form Critics imagined that no one cared to write anything down because they believed Jesus would return so soon there was no time for writing books. The assumption is, Jesus wrote nothing and neither did his disciples. In fact, the disciples are often described as illiterate peasants who could not have written down his words even if they wanted to! Bart Ehrman makes this point in his Jesus: Apocalyptic Prophet as well has his recent How Jesus Became God. Jesus lower-class peasant followers “spoke Aramaic rather than Greek. If they did have any facility in Greek, it would have been for simply for rough communication at best…Peter and John are explicitly said in the New Testament to be ‘illiterate’” (Jesus: Apocalyptic Prophet, 45).
Nevertheless, there is some evidence for listeners taking notes in order to “capture the gist of speeches” (Craig Keener, The Historical Jesus of the Gospels, 148). He cites a number of ancient sources that indicate some took basic notes for the purpose of guarding one’s memory. Cicero describes Cato as wanting to “read the note-books of Aristotle” over his holiday as a way of refreshing his memory (Cicero, Fin. 3.3.10). Notebooks are not necessary neat collections of texts, some teachings of the stories were “left in the form of note-books. This distinction occasionally gives them an appearance of inconsistency” (Cicero, Fin. 5.5.12). Bird offers several other Jewish and Christian examples in addition to the Roman texts cited by Keener. The practice of testimonia, or thematic collections of scripture was used in the early Church. Justin knew of twenty-six topically arranged collections of sayings of Jesus (Dial Tryph. 15-17, Bird, 47)
These examples are more appropriate for the Gospels, since the disciples were “more like Qumran” than trained scholars in the Hellenistic world described by Cicero! Bird concludes that it is “highly probably that notebooks were used by Jesus’ own disciples and by later adherents in the early church” as a memory aide (Bird, 48). I think Bird needs to contend with the objection that even if later (post-Resurrection) followers kept notebooks, Jesus’ own disciples were by in large illiterate. I think this might be done for a few, perhaps even Peter, James and John. They were not the lowest strata of a peasant society because they appear to have owned boats and had hired men working for them. If they were followers of John the Baptist from the very beginning, perhaps they had been given some synagogue training over and above what a “lowly peasant” normally receives.
If this is the case, then jotting notes about the words of Jesus to use in later teaching and preaching is not too-farfetched. I doubt they had their hipster moleskines, anything written would have been to aide memory. The upshot of all this is that the source of the Oral Tradition sought by Form Criticism is the disciple of Jesus who listened carefully and remembered, and perhaps wrote a few notes as well.