What should the ideal student-teacher ratio be in a nursery class?

According to the Ministry of Social & Family Development, the staff to student ratio is 1:12 for a teacher without an assistant or 1+1:18 for a teacher with assistant. This is for Nursery 1. For older children, the student ratio increases. Personally, I feel that there should be at least 2 teachers for Nursery classes as it is difficult for one teacher to mind so many children. http://app.msf.gov.sg/Press-Room/Better-Support-for-Child-Care-Teachers