You can get a lot of use out of the several LookUp functions built into ClarisWorks (any version). Here is a useful example.
You have a list of grades in number format and you'd like to 'look up' each one's corresponding letter grade. We'll use the vertical LookUp function, VLookUp.
The Formula in cell C3 is =VLOOKUP(B3,$E$6..$F$11,1). Since the references to the LookUp table itself ($E$6..$F$11) are preceded by dollar signs, it makes this an absolute reference to this location. Therefore, you can (under the Calculate menu) Fill this formula Down the column to get the rest of the grades. (Note that in any LookUp table, the numbers must be sorted in ascending order).
If desired, the column with the numeric scores could be collapsed to a 0 width - the formulas in the next column will still function. The lookup table, though it must be on the same spreadsheet, need not be visible or printed. (The 'Count2' function could then be used as well to add up the total number of A's, of B's, etc contained in the range of computed grades.)