We have had several faculty who wanted to make the grammar check feature available to their students before their papers are due, much like the originality reports. We discovered just before break that the student only has access to the grammar check once a paper is graded; The Grademark/grammar feature is not designed for the students to use to review their work before submitting, but to ease the grading and markup burden for faculty.
But there is a workaround! The workaround is to create a draft assignment with 1 point assigned to it. It does require that you at least review the paper and assign the point for it to be returned to the student as graded. On the “graded” version they will be able to see the grammar check, then they can incorporate that feedback into their final version for grading.