Almost every preschool website lists a number somewhere — "small class sizes," "low ratios," "8 children per teacher." Parents tend to glance at it, nod, and move on to photos of the classroom. It's treated as a checkbox, not something worth actually understanding.

That's a mistake, but not for the reason most people assume. The research on class size in preschool programs isn't a simple "smaller is always better" story. It's more specific than that — and understanding the specifics is what actually helps you tell a good program from one that's just using a good number.

Class Size and Ratio Are Not the Same Thing

This is the part that trips up most parents comparing preschool programs: "class size" and "staff-to-child ratio" sound interchangeable but describe two different things.

Ratio is how many children each educator is responsible for — say, 1 teacher to 8 children. Class size (sometimes called group size) is the total number of children in the room, regardless of how many staff are in it. A room with 16 children and two teachers has the same ratio as a room with 8 children and one teacher — 1:8 — but it's a very different environment. More children in a room means more noise, more transitions, more competing needs, even when the ratio on paper looks identical.

Research has found that these two factors can behave differently — they're related, but not interchangeable, and a program can score well on one while being unremarkable on the other. A centre that only advertises its ratio without mentioning group size is telling you half the story.

What the Research Actually Shows

The honest answer is: it's more complicated than either "class size doesn't matter" or "smaller is always better," and a lot of what's out there overstates one side or the other.

One of the earliest and most influential studies — a 1979 study that's still cited today — found that children in smaller preschool classes showed larger gains in general knowledge, language, and social behaviour compared to children in larger classes. That result helped shape a lot of the "smaller is better" thinking that's stuck around since.

But subsequent research complicated that picture considerably. Plenty of later studies found no consistent relationship between class size and child outcomes at all. A large meta-analysis pulling together decades of program evaluations found something more specific: the relationship isn't a straight line. For child-teacher ratios around 7.5-to-1 or lower, reducing the ratio by even one child predicted a meaningfully better outcome. For class sizes of 15 or fewer, the same pattern held — one fewer child mattered. But above those thresholds, the analysis found no discernible benefit to shrinking things further. In plain terms: going from a class of 30 to a class of 26 doesn't seem to do much. Going from 9 children per teacher to 7 does.

That threshold pattern matters, because it means the "smaller is always better, no matter what" marketing framing isn't quite accurate — but neither is dismissing class size as irrelevant. The honest version is: below a certain size and ratio, shrinking further has a real, measurable effect. Above it, you're mostly paying for a number on a brochure.

Where Class Size Actually Shows Up in Behaviour

One of the more consistent findings isn't about test scores — it's about behaviour. Programs with higher child-to-teacher ratios report meaningfully higher rates of expulsion and suspension than programs with lower ratios. One national study found that classrooms with a ratio around 12-to-1 reported child expulsions at roughly 12.7%, compared to about 7.7% in classrooms closer to 8-to-1.

That gap makes intuitive sense once you think about what a teacher managing 12 or more young children alone can realistically do in the moment a conflict starts. There's simply less capacity to step in early, de-escalate, and redirect before something turns into a bigger incident — which means more incidents get labelled as behaviour problems that, in a smaller group, might have been caught and handled before they became one.

Smaller, well-staffed groups have also been linked to lower reported teacher stress and stronger teacher-child relationships — which matters because a stressed, overstretched educator has less bandwidth for exactly the kind of individualized attention that makes a preschool program good in the first place.

Ontario's Regulated Numbers for Preschool 

In Ontario, both ratio and maximum group size are set out in Schedule 1 of Ontario Regulation 137/15 under the Child Care and Early Years Act (CCEYA). For a preschool-age group (roughly 30 months to 6 years), the maximum ratio is 1 staff member to 8 children, with a maximum group size of 24 — meaning a fully enrolled preschool room could have up to three educators and 24 children in it at once.

That's the legal ceiling, not a target. A program running well under that maximum — say, 16 or 18 children instead of 24 — is operating with meaningfully more room per child, literally and developmentally, even though both would be technically compliant.

What to Actually Ask When Comparing Preschool Programs 

Given all this, the useful questions aren't "what's your ratio" — that's on the website already. Better ones:

What's the actual group size in the room my child would be in, not just the ratio? Ask for the real number, not the licensed maximum.

Is the room ever run at or near its maximum group size, or does it typically run under capacity?

How many educators are in the room at once, and does that change throughout the day?

What does the room look like during a transition — arrival, lunch, nap setup — when the group is at its largest and most active?

A program that answers with specific, real numbers (not just "we follow all provincial regulations") is one that's actually thought about this, rather than treating ratio as a compliance checkbox.

Common Misconceptions Parents Have

"Lower ratio always means better care."Only up to a point. Below the research thresholds — roughly 7.5:1 for ratio, 15 for group size — shrinking further hasn't shown a strong additional benefit. Above those points, other things (teacher training, curriculum, continuity) likely matter more than shaving off one more child.

"A program advertising a great ratio is automatically well-run." Ratio without context about group size can be misleading, and a strong ratio on paper doesn't guarantee experienced, well-supported staff.

"Bigger classes are only a problem for learning." The behavioural data is arguably the stronger finding here — expulsion and suspension rates track pretty closely with ratio, which affects a child's experience regardless of how their test scores would come out.

"This doesn't matter once kids move past preschool age." It matters differently, not less. In before and after school care, group sizes scale up considerably under Ontario regulation — up to 1:15 or 1:20 for older school-age groups — and the same logic about a teacher's actual capacity to notice and respond to individual kids still applies, even though the numbers look different than they do in a preschool room.

St. George Mini School keeps preschool group sizes well under Ontario's licensed maximum across all three Preschool in North York locations, with consistent, RECE-led classrooms. Book a tour to see an actual classroom, not just the ratio on paper.