The seventh-graders have been identified as contacts of the confirmed case at school and have been asked to stay home to reduce the possible spread of the virus.
The school is the eighth to be affected by the virus after the children returned last week. You can follow the updates live here.
Cardiff Council said an ‘improved cleaning’ had been carried out on the areas of Penylan School used by the class.
Principal Iwan Pritchard said: ‘Following confirmation that a student at the school tested positive for Covid-19, we have acted as quickly as possible, working with Public Health Wales, to contact all students in the student’s class bubble.
“As a precaution, an additional cleaning, in addition to the daily cleaning regimen that we set up, was also carried out.
“Thanks to the procedures we have in place, limiting contact between the different classes and recording the seating plans of all the lessons, we have been able to limit the number of pupils having to isolate themselves and there is no need to parents or students who have not. contacted for self-isolation or to be unduly concerned.
“After respecting the two-meter social distancing rule, or wearing a face mask if that has not been possible, no school staff member needs to isolate themselves.
“School staff will continue to be vigilant of any student showing symptoms and will take appropriate action if they suspect that a student could potentially have Covid-19. “
Parents of all students identified as contacts were contacted by letter and SMS on Sunday evening.
Councilor Sarah Merry, member of the Cardiff Board of Education cabinet, said: “The safety of students in our schools is of the utmost importance and procedures are in place to ensure that they are also protected possible, but this is a clear reminder that Covid-19 has not ‘gone away and I urge all parents to remain vigilant and ensure their children do not go to school if they develop symptoms. ”
The other latest cases are believed to have occurred at Cymmer Primary School and Pontygwaith Primary School in Rhondda.
Last week, staff at Ysgol Bryn Castell in Bridgend were asked to self-isolate, with the start of term being delayed for some students after a staff member contracted coronavirus.
A staff member from Maesteg School has also tested positive for Covid-19 while cases of Covid-19 have also been confirmed in Ysgol y Dderwen in Carmarthenshire and also at Woodlands Community primary in Cwmbran.
The latest figures from Public Health Wales (PHW) show new cases of the coronavirus in Wales have increased dramatically in recent days.
On Sunday, September 6, PHW said 98 new cases had been recorded in Wales. He is following 77 new cases on Saturday and 51 on Friday.