The switch from two school sessions a day to just one may have educational benefits for pupils and teachers.
But for parents who ferry their children to school by car as well as other motorists, it has heaped further pressure on Singapore's already congested roads.
This year, 29 primary schools have implemented a single session, which begins in the morning. That brings the total number of schools operating single sessions to 155.
Checks by The Sunday Times during the morning rush hour and afternoon dismissal times found roads outside schools jammed with parents trying to drop off or fetch their children.
Traffic on the single-lane road outside Rosyth School in Serangoon North, for instance, came to a crawl just past 7am, before morning assembly, last Wednesday.
Drivers were committing illegal U-turns in order to get to the school gate, and waiting in yellow boxes on their way out of the school.
One parent, a 45-year-old physical trainer whose daughter is in Primary 3 at Rosyth and declined to be named, said: "Now, the whole school is made to start at the same time, so everyone has to be there by 7.20am. There can be no compromise." He added that he has seen at least one "near-collision" in the morning.
Residents in the area trying to get to work also said the jams have worsened since last year.
Mr Joe Tan, 45, a sports television broadcaster, said he often sees two buses from the same service stuck at the same time at the bus stop next to Rosyth. "Parents should try not to drive their kids to school," he said. "They should get them to walk or take the bus."
At Henry Park Primary, around dismissal time at about 1.45pm last Wednesday, there was a queue of more than 80 waiting cars snaking from the school gate and spilling into Holland Road.
Retired businessman Will Yong, 60, who was there to pick up his two grandchildren, said: "Imagine two sessions of kids, and all of us rushing to school at once. The crowd is unavoidable."
When asked why he chose to brave the crush, he said: "The school bus picks them up early and drops them off late. They're too young for public transport so it's dangerous for them to take the bus on their own."
Congestion appeared to be less of a problem at other newly single-session schools like Gan Eng Seng Primary in Bukit Merah, though parents there said it is now more difficult to find parking spots.
Oil and gas technician Rahman Abdullah, 42, said: "During the double session, there wasn't so much of a traffic jam but, nowadays, I have to come 45 minutes early so I can find somewhere to park and wait for my daughter."
A Ministry of Education (MOE) spokesman said: "Schools that transit to a single session may experience heavier traffic conditions during school peak hours. Prior to a school transiting to a single session, MOE will commission a traffic impact study.
"For schools with significant vehicular traffic, where feasible, a transport hub would be built to better contain the traffic within the school and to facilitate drop-off."
Some school principals said they are working closely with the Land Transport Authority (LTA) to address the traffic situation.
Henry Park, for instance, is deploying additional wardens to direct traffic flow. Rosyth has informed residents in the neighbourhood about the school's traffic measures.
An LTA spokesman said most school sites have limited space to accommodate the surge of traffic during busy periods.
She said: "At some schools, the agencies will also jointly work with the school and community to issue advisory letters and information to guide parents and road users on proper road behaviour, and provide advice on alternatives for parents to alight and pick up their children."