Businessman Cheng Heng Heng attended his first ballot for Primary 1 vacancies yesterday - and had to worry about not one, but two, of his three children.

The 40-year-old applied to enrol his six-year-old son and daughter - born 11 months apart - for registration at Nan Hua Primary School, which was oversubscribed in Phase 2A2, for kids whose parents or siblings are former pupils, or whose parent is a staff member.

When the phase closed on Tuesday, the school in Clementi had 43 children vying for 37 spots. Those who are Singapore citizens and living within 2km of the school secured their places. The other Singapore citizens had to ballot for the remaining vacancies.

In such ballots, siblings are treated as one unit and share the same number. If it is picked, they will be admitted. If not, both lose out.

Mr Cheng said: "As the ballot went on, I knew the chances of getting my kids into the school were getting slimmer." He breathed a sigh of relief when the pair's number came up after 10 children.

Nan Hua was one of five oversubscribed schools to hold ballots for Primary 1 places yesterday. The others were Red Swastika School, Ai Tong School, Catholic High School and Henry Park Primary. Nanyang Primary did not conduct a ballot despite being oversubscribed as all 55 Singapore citizens secured places.

Registration for Phase 2B starts on Monday. Last year, 28 schools held a ballot . This year, 13 schools each have fewer than 30 places.