A metaphor sometimes used in teaching discipline-based academic writing is that the experience of learning to write in various academic contexts is like learning a new language (L2). This approach is critically examined here, and its implications for "writing across the curriculum" (WAC) programs at the college level are discussed. It is argued that uncritical use of the metaphor can mask the difficulties of learning a second language and lead to marginalization of second-language writers in WAC programs and in the professional discourse of composition studies in general. In addition, it is proposed that specialists in both WAC and English-as-a-Second-Language have much to learn from each other. Mutually beneficial ways of achieving interdisciplinary collaboration between the two fields are considered. (Contains 14 references.) (MSE)