The Independent Schools Inspectorate (ISI) – a watchdog for independent schools – has asked Ellesmere College to take action over its findings in relation to pupils who take part in the Ellesmere Titans Swimming Club.
It has called for "immediate action" to address the issues.
The report follows a Swim England investigation into the swimming club earlier this year which saw two coaches suspended over "welfare issues" and "a complete change of the governance structure" at the club.
That investigation was launched after parents raised concerns.
The club, which is associated with the school but run independently, uses some of the school facilities and trains some of its students. The college is planning to take over the running of the club, a process it hopes to complete by the end of term.
The club has previously enjoyed a glowing reputation, training a series of international standard swimmers – including several who competed at the recent Tokyo Olympics.
The ISI's report said that following the Swim England investigation it was not satisfied that the college was ensuring its pupils are in a 'safe environment' when at the swimming club.
But in a letter to parents, the college's headmaster Brendan Wignall expressed "surprise" at the conclusion.
The report stated: "The school fails to ensure that it provides a safe environment in which children can learn while they are taking part in the activities of the swimming club which the school permits to use its facilities and which it enables pupils to join.
"The annual review of safeguarding does not include adequate consideration of the safeguarding of pupils while they are taking part in the swimming club.
"The school does not make effective assessment of the potential risks relating to pupils’ participation in the swimming club including those relating to staff involvement in the club."
The ISI has provided three recommendations for the school to be addressed immediately.
In his letter to parents Mr Wignall said the recommendations had come after the second of two inspections this year – the first which he described as "entirely positive", but said could not be published.
He said: "To be honest it has been a frustrating time. The relationship between the college and the Titans has not changed since the Titans was established over 10 years ago: it has been our intention mostly to take over the management of the Titans and incorporate it into the school's management structures (for reasons entirely unrelated to all of this business), but Covid got in the way of implementing that plan.
"It is a plan that we are in the process of working towards implementing now and hope to have completed by the end of this term.
"We were surprised that we were found non-compliant, given that nothing has changed and that we have passed previous ISI compliance inspections."
Mr Wignall said that the college would carry out a number of measures, including a formal review of Titans' polices and procedures with regard to safeguarding.
He added that there would also be changes to the minute taking system for school council meetings on safeguarding matters related to outside clubs – to provide greater detail, as well as written risk assessments to work out any risk to pupils being members of the swimming club.