Spellcheck, OP. You need to get one. There is no reason why anyone old enough to be legally on this site to mispell some of the words you did. (I will give you a pass on unconcious (unconshus) because it can be a tricky word, but the rest were elementary words that you should have learned by now). Go read books. I know we don't often tell people this, but also look at picture books. They do have what your story is missing: a point.
Just for shits and giggles, I fixed what you wrote. Below yours with spelling errors and questions highlighted. I did go through and rewrote everything you had, but I decided to not post it, feeling that it was too cruel and mean. If you are interested, I can PM you a rewritten copy of your work for you to look at.
Everything was loud and chattery in the classrom on this fine Monday morning. Kayleigh was running late for school again. She quickly ran into the cloakroom and put her things on her peg as quickly as she could. Modern American schools don't have cloakrooms. If this story takes place elsewhere, it's best to let the reader know that. A few Gaians are from America, and it is a default to put the mindset of reading in one's own culture. I don't know if England schools still have cloakrooms (and I'm old enough to know what they are), but a setting would be nice.
When she did she walked into the classroom quickly. You have used quickly three times in the past two sentences. Take two of them out. She walked past Ben the school pranker. There really is no such thing as a school pranker. Schools are often too big to have a "school pranker". A prankster is one thing, but you make it sound like an official title. He put his foot out as Kayleigh was walking past and she tripped over. Kayleigh was unconciousfor a few minutes. Writing fail. If any student is unconcious for a "few minutes", the teacher would have called for the school nurse and possibly an ambulance. Being unconcious would be an indication of something seriously wrong. They would not just leave her on the ground and pretend it never happened. When she woke up she was still on the floor and everyone was crowded round her staring at her even Ben.
''You tripped me up you flamin idiot,'' shouted Kayleigh to Ben. Flaming idiot? He's gay? Also, a "!" and "shouted" mean the same thing. You don't need both.
''No, I didn't. You tripped over my chair,'' lied Ben.
''No. I saw you put your leg out and I tripped over it,'' explained Kayleigh. Don't capitalize your dialog tags.
Kayleigh stood up slowly and kicked Ben in the leg. Ben fell over in pain. ''Now you Know how it feels,'' cried Kayleigh.
Ben was crying on the floor in pain. ''God you have a good kick girl,'' cried Ben. And that has to be the dumbest reply to being kicked in the shin I've ever read.