The college in Leyland has today (September 15) confirmed that three of its students have contracted COVID-19.
They are now at home and self-isolating, along with their classmates and other close contacts at the college.
Runshaw said all three students are coping well and are only experiencing mild symptoms.
It said its track and trace system was swiftly put into action to curb the spread of the virus.
A spokesman for Runshaw College said: "I can confirm that we are aware of 3 isolated cases of COVID-19 in our students.
"All have identified the likely cause of infection in their personal lives and thankfully all are experiencing only mild symptoms at this stage.
"Our isolation process is working very effectively. We have reported each case to Public Health England and have carefully followed their instructions.
"Each of the cases are now self-isolating for 14 days, following the guidance.
"In addition, we have identified their close contacts and potential contacts.
"Those people have all received a notification letter. As a result, one class of 18 students is now self-isolating but are continuing their full-time studies online, providing they do not become unwell.
"They continue to be supported by our excellent team of Progress Mentors, as well as their teachers."
Runshaw College joins a number of schools in South Ribble that have confirmed cases of coronavirus among its student body.
St Mary's Catholic High School and Leyland Methodist Infant and Junior Schools, as well as Hutton Grammar, have all sent children home after pupils tested positive.
In Preston, Cardinal Newman College sent dozens of students home last week after a student tested positive, and a number of classrooms had to be closed for a deep-clean.