motivation for students

Today, I figure out that my students lack of motivation to study and they try to fool with me. They are in their fifth grade, but only one manages to finish the math as counting some divisional problems. During my instruction, some of them are running around the classroom. They lack of disciplines from family, school, and individul. Until now, I have only two weapon toward them, one is giving them refreshment, and another is sending them to school for immediate punishment. Children grow up and learn from environment. I can't do much things about their behaviors. I just to help with my best efforts. School have to educate them together with their family. What I can do is to remind them the consequences of bad and good things. The authority of school is going down from the point of society. Many students nowadays don't respect their teachers. It is sad, but we have to well behave ourselves. I have to use cookies and candies to promote their motivation. It is sad, but I have no choice. I hope they can get motivation from inside of their mind, not depend on outside rewards. I hope I know how to solve this problem and lead them to the right track in a near future.