Grammar instruction has long been a troubling issue for many language arts teachers. This collaborative research between an elementary classroom teacher and university faculty, based on the assumption that grammar is most effectively taught in reading and writing, looks into the short- and long-term effect of error-based grammar instruction on the writing of a group of fifth grade students. The approach employed in this study is comprised of analysis of grammar errors in student writing, mini-lessons that target those errors, and reanalysis of errors in the follow-up writing. This study found that for this particular group of students, on almost all the grammatical items, accuracy can be improved through mini-lessons that target errors identified in student writing in both short and long-term measurements. Results indicate that mini-lessons that target errors identified in previous students' writing produce positive short- and long-term effect on students' rewriting. An instructional model based on the findings of this study is also proposed.