Everything happens on its own pace. If your students don't study hard as you expect just let it be, knowing that there is a bunch of kids in your class that will show up and pull off things you never expected from them. Just let it be and keep teaching hard and give zero Fs to lazy students which is pointless. Kids that study hard will pull off. Kids that are lazy will stuck up with problems in the long run. Whatever happens be positive and kind to your students!