Caution for Common ault...teaching career?

Two years ago I was cautioned for common ault. I had just started uni and ended up getting too drunk. When a bouncer tried to kick me out of the nightclub I struggled and ended up hitting him in the face. He was in no way hurt but the police were called. I now want to apply for a PGCE (teaching course) and I'm worried that the collge will refuse me straight away when they see my record. How long does a caution last?