One elementary school writing sample written to cue under a 5-minute time limit was presented to 33 teachers who had been trained to use a holistic and a primary trait writing sample assessment system. Working on the assumption that teachers would recognize mechanical errors on sight, training in mechanical control was limited to orientation regarding the mechanical targets to be counted: capitalization, punctuation, single word errors, and structure. Error tallies indicated that while 70% of the teacher/scorers tallied within central tendency, the other 30% to 40% tallied beyond central tendency, indicating that they did not recognize errors. No error count was agreeable to all readers. Using single word errors as an example, eight teachers failed to recognize some combination of missing periods, missing commas, missing apostrophes, and inappropriate comma use. If teaching writing well has anything to do with helping students master the basic mechanical conventions, the teachers' ability to use those conventions in their own writing is necessary, but insufficient. Clearly, there must be a parsimonious conception of high-utility mechnical conventions in preservice and inservice teacher education. Further, these conventions must be taught directly, practiced in writing, and recognized as instances and noninstances in a variety of actual student writing samples. (HOD)