You bet your bottom dollar they do.  Actually, I just put together a new page for Male Enhancement Magazine about a new clinical study that is currently in progress on this very subject - Best penis enlargement exercise programs. 

The clinical study is aimed at having several test subjects, men looking to increase the length and girth of their penis through exercise, complete specifically “prescribed” penis exercises at least 4 times per week. 

They are going to measure the results at the end of course, but already the results are incredibly promising.  The subjects are going to complete a full six month assessment, and they are of mixed race, gender and age. 

They are also being asked to rate their sexual satisfaction as well as penis size satisfaction periodically so researchers can see how these exercises are faring in that arena as well.

With specific, clinically backed penis enlargement exercises, you can achieve up to a 3″ penis size increase according to many who have tried it and/or studied this modality of size increase.  Interesting stuff, to say the least.