Working in schools can be a can of worms, if you do not check on a few things first. If the school is still fully with the local authority they will most probably come under the local authority requirements. This might be the work has to be carried out by a member of either the NICEIC or ECA, or the certificates have to be either NIC or ECA. Whilst this is, as previously pointed out, almost a form of restrictive practice, they will tell you it is because of the additional bonding (financial not earth) or the recourses available in the event of problems.
If the school is totally responsible for its own finances and management then they can decide what they want to do themselves. This opens the door for the sparks who is not a full member of either of the big organisations and certificates issued at the end of carrying out the work should be accepted. They may require you to give references and produce your insurance details but that should not create a problem.
It's good work if you can get it.
Showing a sign of the times, you may also be requested to provide full personal details of those to be working on the school site, in order that checks can be made regarding sexual offenders etc.