A baby boom, inward migration and a stagnant housing market means extra spaces will have to be found until at least 2022/23.
On Monday, the council revealed which schools would be next to take additional classes or be permanently expanded to create 660 extra primary places for this September.
Estimates based on Croydon's population growth over the last two years show space may have to be found for up to 53 reception classes – or 1,590 children – by 2016/17.
Research now shows the extent to which this intense demand for primary places will put our secondary schools under pressure in the future – with a potential 96 forms of entry for 2,880 pupils needed in a decade's time.
Tim Pollard, cabinet member for children, young people and learners, believes the projections will give the council the edge when it comes to meeting this demand.He said: "There are quite a lot of unknowns but what we're doing is putting in place additional capacity based on hard evidence, a flexible system based on permanent expansions for what we absolutely know will happen and bulge classes for anything on top of that."
Croydon Council recruited a specialist external research company to revise its own estimates of the demand for school places.
The new predictions are based on the Office for National Statistics' birth data, school pupil counts and transfer rates, London Assembly population projections and housing data.
Three scenarios were developed; the first based on growth continuing in line with birth rates, the second on the average level experienced over the past five years and the third at the higher rate experienced in 2011/12 and 2012/13.
Current levels of demand make the first scenario "very unlikely".
Projections based on the final two outcomes show the council will need to find between 8 and 18 additional forms of entry for 2013 – 240 or 540 places above the 5,100 offered in 2012.Cllr Pollard believes the reality will be closer to the second scenario of growth, continuing at the average rate experienced in the past five years.
But the council must also plan for the worst-case scenario. At Monday's cabinet meeting it approved the creation of 22 new forms of entry in September 2013, based on early analysis of primary applications received before the deadline earlier this month.
Eight of these will be created by permanently expanding seven schools, and 14 others through bulge classes, mainly at Roman Catholic infant schools and nurseries.
This is on top of the 240 additional permanent primary school places, including a new academy, 540 bulge places and Special Educational Needs bases at nine schools made in 2012/13.
Plans are already under way to create the extra secondary capacity produced by the boom at reception level. Two new schools are in the pipeline, with the council actively inviting submissions from free schools and academies.
If upper growth estimates prove correct then the first extra class will be needed at secondary level from 2014/15.
Two years later, nine extra forms of entry will be required, with demand peaking at 19 additional classes (570 pupils) in both 2019/20 and 2020/21.
Kathy Bee, Labour's education spokesman, said funding rather than finding the extra places is her biggest concern.
This year's expansion plans will cost £19.85m assuming the council can secure funding for two free schools.
She said: "I've become slightly numb to the numbers because they've been so big for so long, but I'm worried by these projections because of the length of time the problem will go on for.
"If you look at the worst-case scenario, the amount of space we will need is really worrying.
"To some extent the pressure on our secondary schools is manageable. It's easier to plan for because we know what to expect as pupils come through the system.
"The concern is the cost. Given the amount being spent on creating extra school places, the council won't have capital available for anything else."
Cllr Pollard is confident that the new projections will mean Croydon gets a fairer share when next year's funding is announced by the Department for Education at the end of month as expected.
"When these issues started it wasn't initially clear where the pressure was going to be," he said.
"But I think it's fair to say the Government is now under no illusion that the pressure is highest in London.
"Croydon's case has been made very strongly within that, so I hope we will see a very significant contribution."
Expansion plans for 2013/14 Permanent expansions:- Downsview Primary and Nursery School, Upper Norwood (one form of entry);
- Norbury Manor Primary School, Norbury (one form of entry);
- Howard Primary School, South Croydon (one form of entry);
- Parish Church Nursery and Infant School, Croydon (one form of entry);
- Forestdale Primary, Forestdale (one form of entry);
- Whitehorse Manor, on its Brigstock Road annex in Thornton Heath (one form of entry); and
- Oasis Academy Shirley Park on Stroud Green Lodge (two forms of entry)
- St James the Great RC Academy, Thornton Heath (one form of entry);
- Ark Oval Primary Academy, east Croydon (one form of entry);
- St Chads RC Primary School, Selhurst (one form of entry);
- Margaret Roper RC Primary School, Purley (one form of entry);
- St Mary's RC Infant and Nursery School, West Croydon (one form of entry);
- St Joseph's RC Infant and Nursery School, Upper Norwood (one form of entry);
- Robert Fitzroy Academy, Addiscombe (two forms of entry); and
- Wolsey Infant and Nursery School, New Addington
