This study examines the writing of 30 engineering students, faculty response, students' reading of the response, subsequent revision, and faculty evaluation to ask what factors contribute to constructive conversation about writing. It affirms previous research that suggests engineering faculty do not provide the facilitative commentary widely believed to promote revision, but argues that faculty commentary may be more appropriate than it appears, especially if complementary activity in the larger activity system is taken into consideration. It further suggests that to teach any genre well, faculty need to reinforce general principles in slightly altered contexts, exposing both choice and constraints. Offering directive comments in slightly altered contexts over time may be more important than simply offering facilitative commentary in stand-alone writing classes. Surprisingly, even very directive commentary can elicit rhetorical thinking in a robust, disciplinary activity system.