The question of whether written genres can be learned through explicit teaching or can only be acquired implicitly through writing in authentic contexts remains unanswered. The question is complicated by the different parameters associated with teaching genre to first- or second-language learners, to children or adults, in settings in which the genre is authentically used or in settings (such as writing classes) in which genre learning is decontextualized. Quantitative studies of teaching genre offer mixed results, but in particular, there are no control-group studies of first-language adults. In this paper, we report research on teaching the genre of the laboratory report to first-language university students in biology labs. In this posttest-only control-group study, the treatment was the use of LabWrite, online instructional materials for teaching the lab report. We hypothesized that the treatment group would be more effective in: (1) learning the scientific concept of the lab, and (2) learning to apply scientific reasoning. Results of holistic scoring of lab reports for hypothesis 1 and primary-trait scoring for hypothesis 2 showed that the lab reports of the LabWrite students were rated as significantly higher than those of the control group. A third hypothesis, that students using LabWrite would develop a significantly more positive attitude toward writing lab reports, was also supported. These findings suggest that first-language adults can learn genre through explicit teaching in a context of authentic use of the genre.