Take informal steps first
You should try to resolve complaints informally and promptly. Careful communication with parents at this stage can stop the flow of consistent complaints and prevent aggressive behaviour.
The first step usually involves a face-to-face meeting (where possible) with the complainant, the subject of the complaint, and appropriate senior leaders. To help resolve the issue, you could ask the following people to also be present:
Use your own judgement about who should be at the meeting. This will depend on how severe the complaint is and what steps will be appropriate to address it. If a