Analysis of Ontario Primary School Class Sizes Part Two: Examining Split Classes

by Joseph Ryan Glover


To practice my skills as a data analyst I decided to look into some of Ontario’s Open Data data sets. The primary school class size data set interested me because I have children in the primary grades and the topic is often in the news. 

Summary of Analytical Findings

  • Public school split classes have increased from 47% of all classes in 2007-08 to 54% of all classes in 2013-14 while Catholic school split classes have increased from 27% in 2007-08 to 48% to 2013-14.
  • Counting only classes with a JK or K student, Public school split classes have increased from 73% in 2007-08 to 89% in 2013-14 while Catholic school split classes have increased from 26% in 2007-08 to 74% in 2013-14.
  • In 2007-08 30% of Grade 1, 2 and 3 classes had 18 or fewer students while in 2013-14 that number is down to 23%.
  • Grade 1, 2 and 3 mean class size has grown slightly from 19.1 students per class in 2007-08 to 19.3 students per class in 2013-14. The standard deviation for class size has shrunk from 1.99 students in 2007-08 to 1.75 students in 2013-14 which indicates that both large classes  (>20 students) and small class (<20 students) are becoming less common.
  • On average, since the 2007-08 school year, 9% of public school board split classes with 19 or more students have been split with 4 or fewer students from a different grade. The Catholic school board has averaged 11% over the same period.

Introduction to the Analysis

As discussed in Part One of this analysis, I have a child in the primary grades in Ontario and I am interested in how the Ontario Government is working to enact its 2003 class size reduction initiative (PDF) which sought to have 20 or fewer students in 90% of all primary classes and 23 or fewer students in every primary class by the 2008-09 school year. While part one of my analysis focused on examining claims made by the government regarding class size, part two focuses on split classes, or classes that contain students from more than one grade.

A First Look at Split Classes

The following chart illustrates the percentage of split classes in the public and Catholic school boards between the 2007-08 and 2013-14 school years. The percentage is calculated by dividing the number of split classes each year by the total number of classes for the year, for each school board. The analysis includes every class in the Open Data data set, not just the Grade 1, 2 and 3 classes used in Part One of the analysis.


The chart shows a gradual increase in splits for the public board and a marked increase for the Catholic board. Considering the rise of all day kindergarten I decided to look at only JK and K split classes. This resulted in the following chart:

jk and k split classes

Which reveals that since 2007-08 the Catholic school board has embraced split JK and K classes and this shift is what accounts for the majority of their 21 percentage point gain in overall split classes since 2007-08.

When looking at splits where JK and K classes are excluded we see a gentler increase that has actually decreased in 2013-14 from earlier highs.

non jk and k split classes

The Impact of Splits

Based on the results from Part One of the analysis the Ministry has been almost entirely successful at eliminating large classes and it seems that creating more split classes is one way they achieved this result. To their credit they acknowledge this point on their FAQ page.


To my reasoning, if split classes are able to help reduce the size of large classes than that means there must be excess capacity available to absorb those students (i.e. space to make a split). This thought led me to examine the trend in class sizes distribution between 2007-08 and 2013-14 and I discovered that small classes used to more prevalent than they are today. For example, in 2007-08 30% of Grade 1, 2 and 3 classes had 18 or fewer students while in 2013-14 that number is down to 23%. In other words, small classes are becoming less common.

Another example of this tendency can be seen in the following table which lists the mean class size and standard deviation (both in units of students) for every Grade 1, 2 and 3 class in each year.


The standard deviations indicates that over time the spread in the class sizes has shrunk as more classes achieve the desired 19 and 20 student class size. What this reveals is that while large classes are getting smaller, small classes are getting larger as they both move towards the desired standard.

The Personal Angle

The whole topic of class sizes and splits piques my curiosity because my son’s grade one class was a split that consisted of 15 grade 1s and 4 grade 2s. A look at the Open Data date file for my son’s school reveals that there was another grade 2 class with 19 grade 2 students and a third class, also a split, with 9 grade 2s and 10 grade 3s. It is noteworthy that all three classes have 19 students and therefore meet the “20 or fewer” guarantee of the Ministry of Education but in order to make it happen four grade 2s had to be housed away from their cohort in a grade 1 class. If those four students were distributed to the other two grade 2 classes their class numbers would have been raised to 21 and the classes would have failed the 20 or fewer test. My question is, was the cost of creating a grade 1/2 split and separating the four grade 2s from their grademates really less than having two Grade 2 classes with one extra student?

I performed one last piece of analysis to try and discover how common asymmetric split classes like my son’s Grade 1/2 split are. By looking only at split classes in Grades 1, 2, 3 and 4+ and then only at splits that have a class size of 19 students or larger and a split size of 4 or fewer I discovered that, on average since the 2007-08 school year, 9% of all public school board splits, or approximately 475 classes a year, have had this level of split asymmetry. The Catholic school board average is higher with 11% of all their splits being highly asymmetrical but due to their lower number of classes it amounts to only about 212 classes a year.

The Ministry published a PDF titled “An Introduction to Combined Classes” that speaks about the benefits of split classes and the reality that even single grades have a spectrum of students with different abilities. I don’t disagree with the points made but my larger concern is about having my child taken out of his cohort, as the 4 grade 2s mentioned above were, for an entire school year. My child will be with his grademates for years, they will be his childhood friends as he grows into his teen years, and I don’t want him to lose a year of social integration so that a school board can meet the Ministry’s class size numbers. This isn’t just my concern either, today was the first day of school and not a single Grade 2 parent waiting to find out what class their child was entering wanted them to be in the Grade 1/2 split. The very idea carried a stigma with both parents and children.