Stowmarket High School has announced it will be not be accepting new Year 12 students in the next academic year as its sixth form is being suspended.
Headteacher Dave Lee-Allan said the school, in Onehouse Road, had not been able to attract enough sixth form students to make it viable to remain open.
He said current Year 11 students had previously been made aware that the chances of them being able to attend the sixth form at the end of their GCSEs were "hanging by a thread".
Stowmarket High School, which is part of Waveney Valley Academies Trust, did not accept new Year 12 students last year as it considered a temporary closure.
That decision has now been made, and Mr Lee-Allan has said the school will support its current Year 11s in deciding where to continue their education.
The nearest sixth form facilities to Stowmarket are located in Stowupland, Ipswich and Bury St Edmunds.
Stowupland High School received permission to build a new £2.4million sixth form block last year.
The news comes after Ormiston Sudbury Academy announced last week it would be "mothballing" its sixth form and temporarily not accept new students as part of plans to reinvest in the school.
The school, which is part of Ormiston Academies Trust, said the closure would allow it to offer "superb provision for post-16 students" when it reopens.
Mr Lee-Allan has said the future of Stowmarket High School is "looking very strong" and it is planning to reopen its sixth form in the future.
He said: "We are not going to be running a Year 12 next year. For a long time now, we have been really challenged by the sustainability of the sixth form.
"Unfortunately, the numbers that came back to use showed that it was just too challenging.
"We said right from the start to all students that the sixth form was hanging by a thread.
"We are going to be suspending it - we want to retain our 11 to 18 status and the future of the school is looking very strong.
"There is strong provision elsewhere, so we have to had to make this decision. We have excellent relations with other partners."
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