Hit by falling student enrolments, 11 schools have merged with others in the last two years and eight of those former school compounds now stand empty.

Three others are being used as temporary premises for schools that are undergoing renovation.

The Ministry of Education (MOE) told The Straits Times it was "finalising plans" for the empty sites, which will be maintained and have security guards posted at them.

The 11 schools had to be absorbed by others because of "falling cohort sizes", said the ministry last year. Without the critical mass, they could not offer a good range of educational programmes and co-curricular activities for students.

Three former schools are being used by others: The former Chestnut Drive Secondary building is now Fajar Secondary until the end of this year; the former First Toa Payoh Secondary building is Pei Chun Public School till the end of next year and the former Clementi Woods Secondary building will be Nan Hua Primary for two years from next year. All three schools were merged with others last year.

If MOE has no plans for a site, it will be returned to the state and put to other uses.

Four more schools are set to be vacated next year when they merge with other schools. They are Bedok North, Bishan Park, Chong Boon and Greenview secondary schools.

Real estate agency International Property Advisor's chief executive Ku Swee Yong said an efficient use of space would be to make the buildings available for other educational needs, such as polytechnic continuing education classes for working adults. "This (could be) a fantastic chance for us to greatly expand our capabilities in education."

Mr Chris Koh, director of estate agency Chris International, said it was unlikely all of the empty school sites would be needed by the ministry, and that some could be handed back to the state. "Some schools are located in mature Housing Board towns that have no space for flats. There's potential for redeveloping them for long-term residential use if HDB takes over."

Some sites of former schools have been used for other purposes. For example, the Academy of Singapore Teachers, launched in 2010, is housed in the former St Andrew's Junior College building in Malan Road. The former CHIJ (Opera Estate) Primary School site in Jalan Khairuddin has been occupied by the Singapore Red Cross since 1991.

There are at least nine other former school sites managed by the Singapore Land Authority that are vacant state properties. They can be rented on a short-term basis for up to 90 days.