Any system you choose needs to be manageable for the organisation and this is written in the GDPR. Some schools, such as special schools, may decide that their students will never have the capacity to understand their data protection rights and will always refer to their parents. In all instances, the consent must be explicit and freely given - so opt in and not opt out. Once you have it, a record needs to be kept so if they are not returning the forms, they are not giving their consent. Applies to staff too. On the mention of consent and staff contracts, if these currently say something along the lines of, 'I give my consent for the school to use my data...' then this needs changing as the lawful basis for using personal data to employ people will no longer be consent, but to perform a contract. All decisions made about how you manage consent need to be documented as this forms part of the accountability principle.