One of the things I tell my student's is not to think of it so much as a "checkride" as an "I agree" ride. I have them read the endorsement for the check/stage ride and it says something to the effect "I (the CFI) find them competent to pass the test." I tell my students you are training to get that endorsement, which says that I, who know your abilities the most, find you (the student) competent to be a pilot. The examiner is just flying with you to see if they agree with me.

Sure it's a bit idealistic but it helps put things in perspective. Does it lower the student's stress? Maybe a few days before the exam but they still go in sweating bullets. I try to down play all checkrides and orals (except CFI initial) that they are just trying to see how much you know and if you can fly the airplane safely. It doesn't mean they shouldn't prepare but it helps with nerves a bit I think.