Why is it important?
Determining employment status is the responsibility of the engager. This means that it is your responsibility to ensure that appropriate tax and National Insurance deductions are made.
If, as part of an audit, HM Revenue and Customs (HMRC) discover that an individual has been incorrectly treated as self-employed, then your school would be liable for the tax and National Insurance that should have been deducted. In addition, fines and interest could be imposed, all of which would be charged against your budget.