How does a 12 yr old girl know if the 13 yr old bad boy in your year likes you he is a rly nice guy but teases me a lot like making pet names for me and smacking my bum in lesson HELPP?

He obiously likes you and is interested. It is up to you if you want to pursure him though obviously sense he is a "bad boy" he may not be the best guy. You should tell him to stop touching you innappropriately and if it continues, tell your teacher.