The capacity limit for physical sports and dance co-curricular activities (CCAs) in schools will be reduced from 50 to 30 people due to the sharp rise in Covid-19 cases in the community.
The Ministry of Education (MOE) said that group sizes should also be reduced from five to two people.
In response to queries from The Straits Times, MOE said last night that these tightened safe management measures will take effect from today.
A circular was sent on Saturday to inform schools of these updates, the ministry added.
Physical education lessons should also be class-based, and consist of individual or group activities up to a limit of two people.
MOE added that in-person CCAs in Term 3 for secondary schools, junior colleges and Millennia Institute had resumed from July 12 and will continue.
The ministry said: "For primary schools, we plan to resume in-person CCA from Term 3 Week 5 (July 26 onwards), but will continue to review if any adjustment is needed based on the prevailing situation."
MOE also said that relevant action will be taken for staff and students, should they or any of their household members receive the "Health Risk Warning" (HRW) or "Health Risk Alert" (HRA) SMS notification from the Ministry of Health (MOH).
Last Friday, MOH said those who have been identified to have visited hot spots at the same time as a confirmed Covid-19 case will receive a HRW via SMS, as part of efforts to aggressively ring-fence Covid-19 cases.
Those who receive a HRW will be required under the law to get tested at a designated testing centre and self-isolate until they receive a negative result for their first polymerase chain reaction (PCR) test.
Those who have visited locations where nightlife establishments operating as food and beverage establishments are sited, or other similar establishments flagged by the Singapore Police Force, will also receive a HRA notice, and should monitor their health and limit interactions with others for 14 days. They are also encouraged to purchase self-test kits from pharmacies.
MOE said it is monitoring the situation closely and will continue to review if any adjustment to safe management measures in schools is needed in line with national guidelines.
Meanwhile, students in Years 1 to 4 at Raffles Institution will be on full home-based learning (HBL) today, after a stall assistant at the school's canteen tested positive for Covid-19.
This is to facilitate deep cleaning and disinfection of the Years 1 to 4 school canteen, said the school in a letter dated yesterday to parents and guardians, signed by principal Frederick Yeo.
The stall assistant had tested positive for the virus on Saturday. She was last in school last Friday and was well then, said the school.
The letter added: "Preliminary information obtained from the stall assistant is that, apart from collecting payment for meals from students and staff, which typically took a few seconds, the stall assistant had minimal contact with them."
The school will be conducting contact tracing, and use information gathered through TraceTogether tokens and apps, to identify students and staff who were in close contact with the stall assistant while she was infectious.
Those who have been identified as such will be placed on leave of absence and then contacted by MOH.
Parents of students who have been identified as close contacts through TraceTogether will receive an SMS or will be contacted directly by MOH with instructions.
The letter added: "We would like to assure you that the school has been and will continue to tightly implement safe management measures. These include cleaning high-touch surfaces regularly and disinfecting our premises regularly."
The letter also said the school will keep parents and guardians updated through the Parents Gateway app.
Several pupils from other schools have tested positive for Covid-19 over the past week.
Yesterday, parents and guardians of pupils at Yangzheng Primary School received a letter saying that a Primary 2 pupil who was last in school last Thursday had tested positive.
In response, all Primary 2 classes will be placed on HBL today and on Wednesday. Tuesday is a public holiday for Hari Raya Haji.
Last Friday, parents of pupils at Naval Base Primary School were told that a Primary 6 pupil there had tested positive for the virus. On the same day, parents at Opera Estate Primary were told that a Primary 6 pupil had also tested positive.
These infections come on the back of a spike in Covid-19 cases in Singapore related to large clusters involving illegal KTV lounges and Jurong Fishery Port.