Up until October 2009 cautions COULD be removed from a person's record after 5 years but there was no compulsion upon police forces to actually do so. However a High Court ruling in that month now means that cautions remain on a person's record for life (or, if we're being really pedantic, to the person's 100th birthday).
While a Supreme Court ruling in November 2010 now means that senior police officers have to allow people to be able make representations about the possible disclosure of ADDITIONAL 'relevant' information under an enhanced CRB check, that doesn't change the rule that ALL cautions (other than those which were deleted prior to October 2009) will now appear on ANY CRB check (at either level).
Since the relevant police force chose not to delete the caution from your record prior to October 2009, it will now continue to appear on any CRB check. All that you can do is to be totally 'up front' about your brush with the law and to include a note about it with any job application which you submit. Having been a teacher myself (and the regional secretary for a teaching union) I know that many teachers have come into contact with the law without it totally 'screwing up' their careers. (i.e. if head teachers and, possibly more importantly, chairs of governors, are aware of such matters at an early stage they're likely to overlook them).
Chris