Four schools in Cardiff have reported cases of coronavirus.
At Cathays High School, 175 Year 8 pupils are self-isolating for 14 days after a pupil tested positive for Covid-19.
One member of staff has also been advised to self-isolate.
Two cases have also been confirmed at Whitchurch High School, bringing the total number at the school to four cases.
In the latest cases, a Year 12 student tested positive over the weekend and all Year 12 students stayed at home on Monday while the contact group was identified.
The school said: "Checks were completed and 20 Year 12 students are self-isolating for 14 days after they were identified as close contacts of the confirmed Covid-19 case.
"All other Year 12 students will return to the school on Tuesday. No members of staff are affected."
The school has also had a positive case in Year 7, leading to 38 pupils in that year self-isolating for 14 days. No members of staff have been affected by this case.
Last week, cases were reported in Year 11 and Year 7 at the school.
A Year 4 pupil at Lansdowne Primary School in Canton has tested positive and 28 pupils have been advised to self-isolate for 14 days. No staff members are affected.
St Mary's Catholic Primary School in Riverside has also been affected with 67 pupils self-isolating after a Year 5 pupil tested positive.
Five members of staff are also self-isolating after being identified as being in the contact group.
To date more than 100 cases of Covid-19 have been reported at 98 schools and one college across Wales since term started in phases three weeks ago.
All Wales' 1,569 schools opened full time to all pupils - except those self isolating - from September 14.
So far 19 of Wales' 22 councils have confirmed coronavirus cases in their schools. Schools do not have to close if a case of coronavirus is confirmed but have to follow protocols set out in Welsh Government re-opening guidance.
