* The contestants may be pre-screened. Before appearing on the show, the contestants may be tested to ensure they have the knowledge of a fifth grader. This would prevent the show from casting contestants who are likely to fail.
* The questions may be carefully chosen. The show's producers may select questions that are easy enough for a fifth grader to answer but challenging enough for adults. This ensures that most contestants have the opportunity to win.
* The contestants may be given assistance. The contestants may be given help from off-screen assistants or producers, such as clues or prompts. This could be done to ensure the show runs smoothly and to help contestants avoid embarrassing mistakes.
Ultimately, it is up to the viewer to decide whether or not they believe Are You Smarter Than a 5th Grader? is fake. However, the above explanations provide some possible reasons for why the show could be produced without being entirely dishonest.