We conducted a post hoc analysis of 771 students’ argumentative writing plans and essays in the Criterion ® database, a digital writing tool, to explore the relations among plan features, essay quality, and writing traits. Students in the study were in Grades 5 to 10 from 68 schools. We found that older students produced writing plans that received higher scores and demonstrated greater genre-specific knowledge than younger students, but regardless of their grade, most students did not consider alternative perspectives or rebut counterarguments in their writing plans. We also found that students’ choice of plan templates was associated with the scores of their plans. Further, factor analysis showed that six of the seven plan feature scores hung together in a single factor (Factor 1) and correlated with multiple trait scores (Factor 2), accounting for most of the shared variance connecting plan scores with writing traits. The “both sides” plan feature loaded on a different factor by its own, suggesting that considering different perspectives is a challenging skill that students may need extra support to develop.