The Ministry of Education (MOE) is keeping a closer watch on children who are not part of the mainstream school system.
Previously, permission from MOE was needed only for Singaporean children who wished to be homeschooled or attend Foreign System Schools such as the Singapore American School.
But smaller, full-time private schools, some of which base their programmes on overseas education models, will also now need to get permission from MOE if they wish to admit Singapore citizens at the primary and secondary levels.
The Sunday Times understands that at least six private schools here are affected by the new rule.
These include Victory Life Christian School (VLCS), Heritage Academy and TLS Academy, all private schools offering the Accelerated Christian Education (ACE) curriculum widely adopted in the US. All are registered with the Council for Private Education, and admit a mix of local and foreign students.
Asked about the new rule, MOE would say only that it "would like all Singaporean children to attend our mainstream schools to acquire a common set of core values, knowledge and skills".
Mrs Jan Boey, 62, VLCS' founder, said she worried about the new rule at first but now welcomes it after seeing that Singapore students who do not fit the mainstream can still be admitted to the school.
"MOE wants national education for all Singapore citizens. It is good for the ministry to know which are the students who pull out from the mainstream, and that there is a place where students who cannot fit into the system can turn to," she said.
Under the Compulsory Education Act, a child must attend a national primary school. Only those with special needs or attending designated religious schools - the six madrasahs for primary school-going children and San Yu Adventist School - may be exempted.
The period of compulsory education is limited to Primary 6. On average, there have been about 50 homeschooled children per cohort in the past five years, the MOE said.
VLCS, located in Balestier Point, has grown from having only 17 students in 2002 to about 130 now. There are currently 42 Singaporean students enrolled in grades seven to 12. They earn an American high school diploma based on their school credits and can take the Scholastic Aptitude Test.
Mrs Boey said: "Some parents feel that their children need a safer environment that teaches values alongside religious education.
"Other children were bullied in school, and did not like going to school, and their parents had to look for an alternative."
Last month, three Singaporean siblings who relocated here after growing up in Japan were given the nod by the MOE to join VLCS.
Mrs Candy Yim, a missionary in her 40s, said she decided to send her three children, aged 12 to 15, to VLCS even though they had considered public schools.
"The standards of English in Singapore are very high, compared to Japan, and my son would have entered the Normal (Technical) stream if he joined a public school.
"Under the ACE curriculum, the students can get school credit for Japanese, and the Christian environment is also good for them."
Heritage Academy in Yishun will welcome its first students soon. Most students are foreigners from regional countries, though a few Singaporean parents have asked about its secondary curriculum.
Said education policy expert Jason Tan of the National Institute of Education: "Mainstream education is seen as a prime means of socialising young people and preparing them for adulthood. The authorities want to regularly monitor students who are not part of the mainstream system. Even one child who slips through the cracks could be one child too many."