Vikkiville - as I've pointed out several times, you DON'T have to be charged for something to appear on a CRB check. Believe me, I do know what I'm talking about here.
There is a section in which the police can put any information they believe is relevant. That information will not necessarily appear on the version of the CRB check that you get - if, for example, you are a suspect in an ongoing investigation the police may not want to alert you to that fact.
The police are contacted for ANY enhanced CRB check - after all, if the applicant is going to be working with children and is currently under investigation for paedophile offences, that would be highly relevant.
What you did would almost certainly not be considered relevant and therefore would not appear on your CRB check. That doesn't mean that all arrests would be considered irrelevant. If you'd been arrested under suspicion of being involved in a paedophile ring, for example, but hadn't been prosecuted for lack of evidence, that information should appear on your CRB check.
By the way, even if your arrest appears on the version of the CRB check which goes to the LA, it would not prevent you working as a teaching assistant.