An actual fifth grader would do well on the television game show Are You Smarter than a 5th Grader. It is fresh in his or her mind, and the material have been reviewed repeatedly. A fifth grader is required to know the subjects. Adults do not retain this information so readily.
Kids are smart these days. The show "Are you Smarter Than A Fifth Grader" features trivia questions from a standard fifth-grade curriculum, and children are great at recalling what they've learned in recent months. Some kids are brighter than others, but I'm willing to bet that with today's common core standards, an average fifth-grader could take the dough.
Are You Smarter Than a 5th Grader is a fun game show to watch, but it features adult participants instead of students. I actually do not think that a 5th grader would win the show easily. My nephew is in 5th grade. Although he is very intelligent, he does not have response times that are as quick as those of an adult.
The show is designed to make the adults feel stupid, and to do that, they find the smartest possible 5th graders that they can find and the trickiest questions that they can find. If they took random 5th graders and put them on the show, a lot of them would most likely struggle. I don't think they would even do better than adult contestants, on average.