John S. Kloppenborg Verbin comments on the Didache (Excavating Q, pp. 134-135):
The Didache, an early second-century Christian composition, is also clearly composite, consisting of a "Two Ways" section (chaps. 1-6), a liturgical manual (7-10), instructions on the reception of traveling prophets (11-15), and a brief apocalypse (16). Marked divergences in style and content as well as the presence of doublets and obvious interpolations make plain the fact that the Didache was not cut from whole cloth. The dominant view today is that the document was composed on the basis of several independent, preredactional units which were assembled by either one or two redactors (Neiderwimmer 1989:64-70, ET 1998:42-52). Comparison of the "Two Ways" section with several other "Two Ways" documents suggests that Didache 1-6 is itself the result of multistage editing. The document began with rather haphazard organization (cf. Barnabas 18-20), but was reorganized in a source common to the Didache, the Doctrina apostolorum, and the Apostolic Church Order and supplemented by a sapiental meditation on minor and major transgressions (3.1-6) (Kloppenborg 1995c). In addition to this "Two Ways" section it is also possible to discern the presence of a mini-apocalypse related to someo f the materials that eventually found their way into Matthew 24-25 (Kloppenborg 1979).
The most obvious insertion in the Didache is a catena of sayings of Jesus (1.3-6) which interrupts the continuity between 1.1-2 and 2.2. The same hand that added 1.3b-6 (and the transitional phrase in 2.1) appears also to be responsible for a transition in 6.2-3 and for the introduction to the apocalypse (16.1-2), which like 1.3b-2.1 Christianizes the earlier document by affixing sayings designed to evoke the sayings of Jesus. It seems clear, then, that the composition history of the Didache involves at least two originally independent documents (Did. 1.1-2; 2.2-6.1; and Did. 16.3-8) which were combined with other materials by an editor into a church manual, and "Christianized" by the interpolation of sayings of Jesus.