Although you can switch any Grade Center column's Primary Display mode to Letter from the Column Information page, sometimes you want students to see both points/percentage and a letter grade for a column. To do this, you'll need to create a Total column that references the original column with the points/percentage value.
To create a new Total column, select Total Column from the Create Calculated Column menu at the top of the Full Grade Center.
Once the Create Total Column page opens, enter a name for the column in the Column Name field, e.g. Letter Grade.
Next, switch the Primary Display mode to LETTER. Secondary Display is not needed.
Under Select Columns, switch "Include in Total" to SELECTED COLUMNS AND CATEGORIES mode to enable the column selection box.
In the Columns to Select menu on the left, select the column you want to be displayed as a letter grade...
... then click on the > button to add that item to the Selected Columns box.
There's no need to change any of the options below the Select Columns section, so you can now hit SUBMIT to add the new column to the Grade Center.
New columns will be added at the far right of the Grade Center table, but you can
rearrange the order of columns using the Manage -> Column Organization menu.