Dear Dick,
You can require student answers to be factored:
http://webwork.maa.org/wiki/FactoringAndExpanding
Also, you should be able to use AnswerHints.pl to provide feedback comments to students who have a correct answer that is not fully factored:
http://webwork.maa.org/wiki/AnswerHints
Good luck!
Paul
WeBWorK Problems
Simplifying Derivatives
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