Commas are primarily used as digit separators for readability of large numbers. Hence they are often recommended when writing sentences. Unfortunately, they also cause a tremendous amount of confusion when used in the machine-evaluation of numbers. The reason is that commas are also used in other mathematical formulas (e.g. ordered pairs, sets, coordinates, etc.) and depending upon the context, the evaluation would be different. Moreover, in an international context (esp. Europe), the decimal point is represented by a comma and not a period.
This is the reason most scientific calculators, computer programs and even AIR/PARCC and SBAC tests do not allow commas in numeric evaluations. At Edulastic, we also follow this convention in numeric questions:
When entering text or constructed responses, teachers should encourage students to write commas .
However teachers should discourage students from using commas when writing large numbers where the expected answer is a numeric response OR a math expression.