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."
More top news
At least two intruders broke into the property and shot Mr Hedger in the early hours of Sunday morning.
Sunday evening's weather for the east
Sunday evening's weather for the west