It accounts for half of their science grade and they spend months making the projects. The judges say they're looking for several different items when they pick the winner.
"Scientific thought, organizational presentation of their hypothesis, as well as conclusions in a clear precise way, so we can understand," said Dr. Alan McQuigg, Judge.
The winner of this science fair will get the chance to compete in Phoenix, Arizona and the prize there is more than $3 million.
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