You can call the kid who is always really nice to the teacher in hopes of getting a good grade a brown-noser or, if you want to sound clever, a toady.
The word toady has a gross, yet engaging history. Back when medicine was more trickery than science, traveling medicine men would come to a town. Their assistant would eat a toad (you read that right) that was assumed poisonous so that the medicine man could "heal" him. Who would want that job, right? So toad-eater, later shortened to toady, came to mean a person who would do anything to please his boss.