Based on your need for a rubric for narrative writing in grade 4, I recommend using Gradescope. This platform allows you to create dynamic point adjustment rubrics, which means you can modify the grading criteria even while grading. This feature is particularly useful if you need to adjust the rubric based on the narratives your students are writing.

Moreover, Gradescope offers AI-assisted grading, which can help you grade written assignments more efficiently. This feature could be beneficial if you have a large number of narratives to grade.

The platform also provides consistent feedback across multiple submissions, ensuring that all students are graded fairly and uniformly. If you decide to change a rubric, all previous grades update automatically, which can save you a lot of time and effort.

Lastly, Gradescope integrates well with learning systems like Canvas and Brightspace, making it easy to add class rosters and push grades to these systems. This could be a significant advantage if you're already using these platforms in your teaching.

Please note that while Gradescope offers a free basic plan, some features may require a paid subscription.