ALEC Hunter Humanities College in Braintree has been branded 'inadequate' by Ofsted.
In a report released last week, the school's watchdog gave the school the lowest grades for the quality of teaching and achievement of pupils.
"This is a school that has serious weaknesses," the report read.
Ofsted inspectors visited the secondary school on Stubbs Lane for two days in October and found that the teaching was far too inconsistent.
"In lessons, such as mathematics, where teaching is weakest, students are not sufficiently interested to work hard because teachers set work that is either too hard or too easy for them," said the inspectors.
"Teachers do not encourage students to think for themselves."
In other lessons teachers were found to stand in front of the class for too long and not let the students get on with practice questions.
"Some teachers do not make the most of students' enthusiasm for learning; they talk for too long instead of allowing students to get on with activities for themselves. In these lessons, students make little or no progress and learning activities lack challenge."
But head teacher Trevor Lawn said Ofsted reports too often generalise on topics like teaching and governance.
"Unfortunately, the inspection process now operates in a manner that tends to produce generalised judgements about areas such as teaching and leadership," he said.
He added that the report "does not give full credit to the good and outstanding work that is demonstrated in many parts of the school".
The inspectors, who sat in on 32 lessons by 30 different teachers, also found that too little homework is set and, when it is set, it fails to stimulate the students' imagination.
GCSE grades have dipped below the national average and, according to the report, only a handful of pupils do better than expected.
"Too much teaching has been weak and has failed to challenge students and extend their learning," the report added.
The inspectors also found that the school's leadership and the safety "requires improvement".
"The governing body is not asking questions that probe and challenge leaders and staff sufficiently about students' underachievement and weaknesses in teaching," said the report.
Mr Lawn added: "We are naturally very disappointed that the ongoing hard work of staff and students, which made us the most improved school in Essex in 2010, has not been reflected in our most recent results and we are determined to return the school to an upward trend as soon as possible.
"Whilst identifying some key weaknesses within the report, we are pleased that the Ofsted inspectors have also acknowledged that the leadership of the school, including the governing body, has the capacity to make the necessary additional improvements that are required."
The 1,000-strong mixed comprehensive received a far better Ofsted report after their last inspection in 2010 – with an overall rating of 'satisfactory'.
In addition, the college hope to win 'academy' status, which would allow them to partner with another school, and has said it will announce its plans in due course.
