Bedwas High School has been placed into special measures by education inspectors.
Watchdog Estyn announced the move following an inspection at the school in May this year.
In its report, Estyn said the school had “unsatisfactory” leadership and that its overall performance was also “unsatisfactory”.
The report reads: “The headteacher has a clear vision for the school based around supporting pupils’ wellbeing and achievement. However, this vision is not shared or understood well enough by all staff and by parents.
“As a result, the school has not succeeded in offering consistently good provision for pupils that enables them to make sufficient and sustained improvements.
“The headteacher and the senior leadership team have not worked well enough together to monitor and improve key areas of the school’s work. These include securing sustained and sufficient improvement in pupil standards, giving a high enough priority to improving teaching and learning and dealing with issues around pupil behaviour.”
Estyn also said that school governors did not challenge the school well enough to improve standards.
The school will now draw up an action plan and will be monitored by Estyn on a termly basis.
Responding to the report’s publication, Bedwas High School headteacher Peter Ward said: “As a school we are surprised and very disappointed with the judgements made by Estyn on our latest school inspection. We’ve received many positive reports from outside agencies, supporting the positive improvements we’ve made over the last three years and our strong exam results in 2016.
“Despite this, we’re already working alongside the local authority to examine carefully the issues raised in the report and to identify the best ways to ensure the school can address the recommendations.
“I’m confident that with the continued support of the Bedwas community, we will do everything possible to build on our progress made to date.”
Caerphilly County Borough Council’s Cabinet Member for Education and Achievement, Cllr Philippa Marsden, said the authority was working with the school to address the report’s recommendations for improvement.
She said: “We’re obviously very disappointed with this news, but we’re already working hard to move Bedwas High School forward. While progress has been made at the school since its last inspection in 2013, we acknowledge that inspectors felt that progress wasn’t swift enough.”
The leader of the Plaid Cymru opposition group on Caerphilly Council also expressed disappointment at Estyn’s report.
Cllr Colin Mann said: “There is a clear need to raise standards because the Estyn report found both the school’s performance and prospects for improvement to be unsatisfactory. Parents with children at Bedwas will naturally be concerned at the weaknesses highlighted and will want to see improvements in performance, which is below or well below similar schools.
“An action plan has now to be drawn up by the school to address the recommendations for improvement and I hope this will lead to a better standard of education for all pupils. I hope the school will be given any support needed to raise standards.”