Because every time we've done this, in every classroom we've done, over and over again, if you go five days into it, there's a group of kids who've raced ahead and a group who are a little bit slower.
因为每次我们做调查， 在任何一个班级， 假设我们拿五天来调查， 都会有一群孩子们领先， 而还有另一群孩子们紧跟其上。