School
ok, from my experience: You have to complete 40 hours at least (more for popular school, like Nanyang Pri, they may call for 80 hours, so check!) So if you count backwards, our 2008 babies will start primary school in 2015, so got to register for P1 in 2014, therefore, you need to complete 40 hours of PV by June 2014. Usually you will start in 2013 for the PV, that means you have to write in to the school to apply for a position to PV in January 2012. Then the school will call you for an interview if you are shortlisted.
For old boy/old gal, your chances are very high cos so far, no school needs to ballot at that stage which is 2A2. But for PV, which falls under 2B, your chances will be enhanced if you live within 1km of the school. For very popular schools like Henry Park, Rosyth, Tao Nan, Nanyang, Pei Hwa Pres, MGS etc, I've heard of parent volunteers who didn't get a place in the school at phase 2B if they live further then 2km, since phase 2B, PVs are also facing competition from Churches/Clans/Grassroots leaders.
Balloting - they will see no of PVs and the no of vacancies. Say there are 50 PVs/churches/clans etc and 30 vacancies, the school will check how many live within 1km. say there are 25 who live within 1km, then this 25 kids will get a confirmed place. Then the school will look at how many live within 1-2km. if there are 2, these 2 kids will have a place. then the 23 PVs/etc will have to ballot for the 3 vacancies left...