You can access an assignment in SpeedGrader directly from the Gradebook.
In Course Navigation, click the Grades link.
Hover over the assignment column header and click the Options icon.
Click the SpeedGrader link.
If you have enabled the Launch SpeedGrader Filtered by Student Group setting, you must select a student group before launching SpeedGrader. To select a student group in the Gradebook, choose a student group in the Gradebook filters.