Inspectors reported of “homophobic taunts” and young women at the colleges not feeling comfortable in common rooms.
Croydon College, which merged with Coulsdon Six Form College in 2019, has hit back at the report.
Bosses say they “feel strongly” the inadequate rating does not reflect the colleges.
Inspectors visited the two campuses in February and published their report on Friday (May 19).
The report said: “A significant proportion of learners who inspectors spoke with do not feel comfortable at college, particularly when using the communal and social spaces.
“While this applies at both campuses, it is more marked for learners at Coulsdon.
“Equally, a significant minority of learners told inspectors they experience homophobic language and taunting and at Coulsdon, female learners do not feel comfortable in areas such as the student common room.”
It went on to say leaders at the colleges have not done enough to create a welcoming environment.
Though, the report added that adult learners at the colleges have a “positive learning environment”.
The inspectors said overall students at Coulsdon have a “poor experience” with the quality of education declining over the past three years.
The report told the college to improve staff training and ensure students have better attendance.
In a joint statement, Caireen Mitchell, principal and CEO Tony Stevenson said they were “extremely surprised and disappointed” at the grading.
They said: “The very mixed profile of the inspection report, with two significant areas rated as ‘good’ and many positive comments about the quality of education and outcomes for all learners, does not align with the final grading delivered.
“Ofsted’s concerns about the behaviours of a small number of learners are not behaviours we recognise on a day-to-day basis at our colleges.
“We raised our concerns directly with Ofsted and provided more evidence to address the areas highlighted.
“In the report, Ofsted acknowledged many challenges faced by the College following the merger that took place just before the pandemic.
“We were very aware of a number of challenges that needed to be addressed but were hampered in our progress by the very real impact of the pandemic.
“However, we are pleased to say improvements have been made and the impact is already being seen in the classroom and the overall experience for learners.
“It is important to note this inspection was based on attendance and achievement data from the first year back in the classroom after the pandemic in 2021/22, which was a challenge for all schools and colleges. It does not reflect the positive standards evidenced in the current academic year.”
They added that the college is “encouraged” its apprenticeship provision is rated ‘good’.
The adult learning department was also rated ‘good’ by inspectors. This is made up of 2,500 people, more than 50 per cent of the college’s students.
The statement continued: “We are focused on looking forward and want to reassure all our students, parents, employers and stakeholders that our senior leadership team, staff and our Board of Governors are wholly invested in securing rapid improvement.”
Ms Mitchell and Mr Stevenson added: “The improvement plan we have put in place is already proving effective, attendance has improved significantly, and achievement has increased by at least 10 per cent at the Coulsdon
“Campus in the January exam series and is on track to reach the national average by the end of the academic year.
“We are disappointed that Ofsted could not take this improved position into account during the inspection, with its judgements being based on historic rather than current data.”