Garrow, Alan J.P. "Chapter Ten: Conclusion: The Compositional History of the Didache." The Gospel of Matthew's Dependence on the Didache. New York: T&T Clark International, 2004, 150-156.
Garrow concludes part 1 of his book by summarizing the five stages he identifies in the Didache's composition. First, he sees the "peri/base" layer. This material gives us the longer title as well as "1.1-5a; 2.1-5.2a; 6.1-7a,c, e, 4a; 9.1-5a; 11.3a, 4-6; 16.1-6, 8-9" (Garrow 2004, 150). Garrow then sees a layer to be added which deals primarily with support and respect for prophets, in 10.1-7; 11.7-9, 12; 12.1-5 (Garrow 2004, 151). To this he adds the modifying teacher layer. This represents an attempt to soften some of the more forceful statements. Garrow identifies these passages as "1.5b-; 5.2b; 7.1b, d, 2-3, 4b; 8.1-2a, 2c-3; 11.1-2, 9-10; 13.1-15.2" (Garrow 2004, 151). The Gospel layer, which inserts claims to the authority of "the Gospel" was later added, accounting for 8.2b; 11.3b; and 15.3-4 (Garrow 2004, 152). The fifth layer Garrow finds is the Jerusalem addition in 16.7 (Garrow 2004, 152). The text of 16.7 does not seem overly important, but it may have provided a buffer between the universalistic interpretation which may have been possible without it and the more selective picture of resurrection which became more common in the Church.
Garrow sees it as absolutely essential that there be at least two layers present in the Didache (Garrow 2004, 153). He closes his chapter with a diagram of the layers he proposes to make up the Didache's text (Garrow 2004, 154-155). Oddly, page 153 is reproduced nearly exactly on page 156, with a section presenting essential conclusions.