Freezing the left column, i.e. column with student names improved the usability of the gradebook grader view.
Scrolling up and down is still problematic.
1. Freeze the rows with the activitiy names and category designations to improve usability when scrolling up and down in grader view.
2. Put the Range row at the top under the activity names and freeze as well. It is logical to have the range for an activity visible along with the activity name.