Recently-adopted standards call for more emphasis on writing in early elementary grades. Rubrics may assist students in attending to important characteristics of effective writing, but research data on their use in early childhood is lacking. This study explores the effects of rubric use on writing instruction of opinion paragraphs for 20 first grade students (9 female, 11 male; 11 Black, 4 White, 4 Hispanic, 1 Asian; 8 English Language Learners) and 12 second grade students (7 male, 5 female; 6 Black, 2 Hispanic, 2 Middle Eastern, 1 Asian, 1 White; 0 English Language Learners) from a low socio-economic Midwestern United States elementary school that was designated a School in Need of Assistance. The stratified-grouped, counterbalanced pretest-midpoint test-posttest study determined if providing a rubric and instructing students on how to use it, in addition to teaching writing mini-lessons regarding specific areas of the rubric, would improve student writing scores compared to the mini lessons alone. Also, data were collected on student attitudes throughout the study. The results indicated that providing instruction on the skills outlined by the rubric, paired with student access to the rubric, improved student writing scores with a large effect size (Cohen's d = 0.92). Although student attitude ratings did not show a significant difference between conditions, student-supplied reasons for those ratings indicated that initial use of a rubric promoted later positive attitudes toward writing and higher self-efficacy while using the rubric. The authors recommend rubric use in writing to assist students in remembering and self-monitoring important components of writing.