This study investigates effects of adjunct writing instruction on undergraduates' technical report writing performance, strategy use, and content familiarity. Employing a mixed-methods approach and a pretest-posttest quasi-experimental design, data were collected from fourth-year mechanical engineering students at Bahir Dar Institute of Technology using tests, questionnaires, interviews, focus groups, and textual analysis. The experimental group received instruction in technical report writing through adjunct writing instruction, while the comparison group received conventional instruction which is non-adjunct instruction. Data analysis utilized one-way MANOVA, independent t-tests, and thematic qualitative analysis. Results revealed significant differences in overall technical report writing performance between the control and experimental groups (Wilks's λ = 0.556, p = 0.000, η2 = 0.444), with statistically significant differences in task achievement, coherence and cohesion, lexical resource, and grammar range and accuracy (p < 0.05). Following the intervention, the experimental group demonstrated better use of technical report writing strategies (Wilks's λ = 0.539, F (5, 58) = 9.903, p = 0.000, η2 = 0.461) and outperformed the control group in rhetorical, cognitive, social, and affective strategies (p < 0.05). Moreover, independent sample t-tests indicated significant improvements in content familiarity among the experimental group (p < 0.05). Qualitative analysis revealed positive perceptions of adjunct writing instruction among experimental group participants, with textual analysis confirming their performance in technical report writing discourse. These findings suggest that adjunct writing instruction is a successful method for teaching technical report writing and research methodology courses at the undergraduate leve