Children in full-day kindergarten are better prepared for school, showing strong language development and better communication and social skills, according to the largest study of its kind in the country on all-day learning.

The findings of an Ontario study of nearly 700 children are an early victory for the province's Liberal government, which has staked its reputation and invested billions of dollars into the early years despite calls to scrap the program and critics characterizing it as an expensive form of government-backed daycare. Still, Ontario's ambitious commitment to roll out full-day kindergarten fully by next fall has school boards worried that cost overruns and an unexpected jump in enrolment would either set them back or force them to move ahead at a cost to other programs.

British Columbia, Prince Edward Island and Quebec offer all-day kindergarten. The Alberta Tories have delayed the program there because of fiscal pressures. Ontario's full-day learning program incorporates two years of a revamped curriculum for junior and senior kindergarten, and emphasizes play-based learning.

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The study released Tuesday found that kids enrolled in the first two years of the province's full-day learning program were better prepared for Grade 1 right across the learning-skills spectrum than those who had only one year in the program. They were also two to four times more prepared than those who never set foot in an all-day kindergarten classroom. Proponents of full-day learning say the results show that more time in the classroom in the early years benefits all students.

"Even though we predicted high impact for kids and families, and also return on taxpayer investment, I never imagined the results would be so dramatic, so soon," said Charles Pascal, the architect of Ontario's early learning plan and a professor at the Ontario Institute for Studies in Education at the University of Toronto. "The program even in its early years of early childhood development is showing that kids' lives are being shaped, and in many cases, saved."

Provincial standardized testing and graduation rates will show whether that will be sustained. Some research into similar programs has shown that the beneficial effect fades, although debate continues.

Evidence is strong that for children from disadvantaged backgrounds, full-day kindergarten can be beneficial in developing learning skills. The Ontario study, however, does not look at specific cohorts. A spokesperson for Education Minister Liz Sandals said that because the program was introduced first in areas identified as vulnerable, and where there was space in schools, it can be assumed that the study represents some of the higher-risk groups. A richer picture of whether the government's investment in full-day learning was justified will come from standardized test scores in 2014 that will assess the math, reading and writing skills of the first cohort of full-day kindergarten students.

The study was conducted by researchers at Queen's University and McMaster University from 2010 to 2012. Educational success at this age is gauged less by literacy and numeracy than through social, developmental and psychological measures, which are harder to measure but are formed in these years, early-learning experts say. Children in the study were assessed by their kindergarten teachers using an early development tool that measures such things as social competence, emotional maturity and language development, classifying pupils as very ready, ready, at risk and vulnerable.

The results showed, for example, that only 4.3 per cent of children who attended full-day kindergarten over two years were at risk of not doing well in Grade 1 because of language skills or cognitive development. That risk stood at 16.4 per cent for those who attended half-day kindergarten. In communication skills and general knowledge development, 5.6 per cent of children with two full years of all-day learning were at risk compared to 7.7 per cent of students who were exposed to the program for one year and 10.5 per cent of children who were not exposed to it at all.

The province is spending more than $1.45-billion in capital costs to expand and retrofit schools, on top of millions in operating dollars. Since the Ontario government introduced it in the fall of 2010, full-day kindergarten has been popular with parents.

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Nadeem Siddiqui said a full-day learning environment will be academically and socially enriching for his four-year-old son, Zain. "If he's doing something in a more structured manner, he will learn more," he said after dropping Zain off at Fraser Mustard Early Learning Academy in Toronto, one of the largest all-day kindergarten schools in North America. The school in north Toronto is welcoming 685 students this week, and is in a dense pocket of buildings that serve as a landing pad for many recent immigrants. Zain had a two-part plan for his first full day of class: colour and play. "It will be fun. There's toys to play with."