Schaff, Philip. "Ch. 26: Authenticity of the Didache." The Oldest Church Manual Called the Teaching of the Twelve Apostles. Second Edition, Revised and Enlarged. New York: Funk & Wagnalls, 1886, 114-119.
In Schaff's opinion the authenticity of the Didache is beyond question (Schaff 1886, 119). There is adequate testimony that it could not have been reated since AD 1056, and it does not favor one or the other party to known conflicts. It appears to have been known and used by Clement of Alexandria and Irenaeus (Schaff 1886, 115). The use continues in Origen and Eusebius, as well as Athanasius (Schaff 1886, 116). "The last mention of the 'Teaching of the Apostles' from personal knowledge was made in the ninth century by Nicephorus, Patriarch of Constantinople (d. A.D. 828), who speaks of such a book as among the Apocrypha of the New Testament, and as consisting of two hundered lines (στίχοι). It turns out that the MS. discovered by Bryennios numbers two hundred and three lines" (Schaff 1886, 118). After this time, the text is not referred to or identified until the late 19th century.