Edward Timpson MP, the Parliamentary Under Secretary of State for Children and Families, has written to East Sussex County Council children's services to raise his concerns.
He wrote: "For a school so comprehensively to fail to protect a vulnerable teenager from a manipulative adult, who has been placed by the school in a position of trust, is an abrogation of leadership and responsibility which had terrible consequences for this child and the family."
He added: "The way that school leaders dismissed warnings made by young people about an improper relationship, and the failure to provide any effective support to the child, is inexcusable."
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Chyna Sullivan, who's 14, was told her hair braids were 'extreme' and 'against school policy'.