Garrow, Alan J.P. "Chapter Eleven: Matthew's Gospel and the Modifying Teacher Layer."The Gospel of Matthew's Dependence on the Didache. New York: T&T Clark International, 2004, 161-185.
Garrow considers that there are points of contact between Matthew's Gospel and the Didache, and that these points may be used to show that Matthew depended on the Didache. The earliest layers, if Garrow's thesis is correct, predate Matthew. Garrow's presumption is that there need be only a credible case that Matthew used the Didache, rather than a case that excludes all other possibilities (Garrow 2004, 1260).
Because Garrow places the Modifying Teacher after other layers in the Didache, his assumption is that if Matthew knew the Modifying Teacher material he knew the whole of the text (Garrow 2004, 161). Didache 14.2 and Matthew 5.23-24 appear closely related. Garrow has previously (chapter 7) oted that the reasoning in the Didache, based on Malachi 1.11, suggests that Matthew's Gospel was not available to the Didache. Therefore, he takes this argument for reconciliation to have come to Matthew by means of the Didache, rather than by any other route (Garrow 2004, 162). Garrow does not offer a credible reason for Matthew to ascribe the teaching to Jesus but to have pulled it from the Didache. He does suggest that Matthew may have taken it from the Didache as a teaching of the Lord Jesus, but this is not a convincing argument in my opinion (Garrow 2004, 163).
Matthew 5.26 and Didache 1.5c place teaching of return of "every last cent" into different contexts, but use the very same phrasing (Garrow 2004, 163). The Didache makes no appeal here to the Gospel, and its context is narrower than that of Matthew. Garrow takes Matthew's use of the statement to be a likely result of Matthew's familiarity with and internalization of the idioms used in the Didache (Garrow 2004, 164).
Didache 8.1-2a, 2c-3 and Matthew 6.5-16 speak of fasting and prayer. They urge distinctions from hypocrites, and teach a similar version of the Lord's prayer (Garrow 2004, 165). The context of the fasting and prayer is different but the language used is very similar. Garrow thinks the differences may be explained by Matthew's confaltion of Mark 12.40-44 and 11.25 with Didache 8 (Garrow 2004, 167). Because Matthew uses almost all the statements of Jesus used by Mark, his omission of 12.40-44 is unusual. However, if he conflated these texts at this point, it can be explained rather easily (Garrow 2004, 168). Garrow further sees it as a procedure consistent with Matthew's tendency to collect, collate, and often conflate similar statements (Garrow 2004, 169). Garrow goes on to describe and illustrate this tendency at length. Garrow's conlcusion is that it is perfectly plausible that Matthew drew on the Didache for teaching on fasting, prayers, and almsgiving (Garrow 2004, 177).
Matthew 5.17-20 and Didache 11.1-2 both speak of the importance of preserving authoritative teaching (Garrow 2004, 177). Those who preserve the authoritative Christian teaching are to be rewarded for their faithfulness. Garrow considers these passages to be so similar they must have a literary relationship (Garrow 2004, 178). However, if the Didache passage is from the Modifying Teacher, that author does not normally draw on the authority (such as the Gospel) for the actual modification (Garrow 2004, 178). This suggests it is much more likely tht Matthew drew on the Didache's reading.
Matthew 28.19 and Didache 7.1c, d, and e speak of trinitarian baptism (Garrow 2004, 179). Garrow suggests that the baptismal formula in Matthew actually came from a smattering of passages from the long title of the Didache through 7.1d (Garrow 2004, 180). While I find this argument somewhat tenuous, it does certainly affirm the possibility that Matthew's interest in the Trinitarian formula was informed by the Didache (Garrow 2004, 181).
Matthew 7.6 and Didache 9.5b both speak against giving holy things to dogs (Garrow 2004, 181). Though the aphorism seems fit for a cultural proverb, Garrow denies finding it elsewhere (Garrow 2004, 182). Both passages make the statement in reference to communion. Matthew's use appears awkward to Garrow, suggesting that it was a quotation drawn in from elsewhere (Garrow 2004, 183).
Finally, Matthew 10.10 and Didache 13.1-2 speak of workers being worthy of food (Garrow 2004, 183). The wording is identical. Garrow does not hypothesize a clear track of dependence for this text. However, again, Garrow suggests it was drawn from a known set of sayings of the Lord by Matthew, who wrote later.
Garrow concludes that Matthew may well have drawn material from the Didache, explaining the similarities at the seven points of contact discussed (Garrow 2004, 184).