The protest will take place between 8:00 and 09:00 GMT to show "support for the teachers and raise awareness among parents," said Mrs Marfell-Williams, who has two children at Reepham.
"It's an injustice that the trust seems to be looking at Reepham to solve its financial problems.
"It serves a huge catchment area; it's the heart of the community.
"It's not just about threatening the future education of children, but the job losses will be a massive blow."
Mrs Marfell-Williams has helped set up parent action group "Stand with RHSC Teachers and Staff" and said it had notched up 500 Facebook followers in five days.
A petition set up by another parent has been signed by more than 1,000 people.
More than 1,000 children, aged between 11 and 18, attend the school, with 749 pupils on Litcham's roll.