Map of Simcoe Muskoka

Early Development Instrument

What is the Early Development Instrument (EDI)?

The Early Development Instrument (EDI) is a survey tool for assessing readiness for school that is completed by teachers for children in their Senior Kindergarten classrooms at a representative subset of schools from all school boards across Ontario. The EDI is produced and provided by the Offord Centre for Child Studies and disseminated and supported by the Early Years division of the Ontario Ministry of Education. The EDI survey has been administered in Ontario on a three year cycle, in 2004 – 2006, 2007 – 2009, 2010 – 2012, and in 2015. The EDI survey was not administered in 2010-2012 in Simcoe County.

For each child for whom a survey is completed, a score is calculated for each domain, the absolute value of these scores is not meaningful. Survey data from the EDI is not designed to be interpreted at an individual level, rather it is designed to be used in describing populations of children, and comparing populations based on their composition (e.g. gender distribution), over time, and across geographies. The EDI uses over 100 questions to assess readiness for school and identify vulnerability across five domains, and several subdomains:

Physical Health and Well-being: Described based on gross and fine motor skills, physical independence which includes general coordination and independence in washroom habits, and physical readiness for school including appropriate energy levels and being dressed appropriately for school.

Social Competence: Based on the child’s curiosity, responsibility and respectfulness, acknowledgement of social courtesies and appropriate public behaviour, self-control, cooperation, adaptability, and ability to follow instructions.

Emotional Maturity: Composite measure of the anxiety and fear levels of children, their tendencies towards aggressive and disruptive behaviour, their attentiveness, their empathy toward other children, and their helping behaviours.

Language and Cognitive Development: Includes measures of age-appropriate numeracy, reading and writing skills, memory, and their understanding of similarities and differences.

Communication Skills and General Knowledge: Identifies whether a child possesses the necessary skills to appropriately communicate their needs and wants, sufficient ability to use language including as part of storytelling and play, and an age-appropriate understanding of the world around them.

Interpreting EDI percentiles

EDI percentiles are calculated based on comparing a child’s scores in each domain to the provincial benchmark, which is based on the data from the Ontario 2004-2006 survey cycle. Three categories are derived from these percentiles:

Vulnerable: Vulnerability is identified where a child scores below the 10th percentile of the provincial benchmark. Vulnerability may be reported by domain, where a child falls below the 10th percentile benchmark for a specific domain, or overall, where a child falls below the 10th percentile benchmark for any of the five domains.

At Risk: Children who score between the 10th and the 25th percentile, compared to the provincial benchmark.

On Track: Children who score above the 25th percentile in each or any domain, compared to the provincial benchmark.

Significant differences in EDI results

As summary data was provided to the health unit for Simcoe and Muskoka through separate agencies, some differences in the analyses were evident.

Significant differences in mean EDI scores are identified based on a difference ≥0.05 in scores across cycles or between Simcoe and overall Ontario results. Significant differences in proportions of the populations identified as vulnerable were based on difference ≥0.5%.

For Muskoka EDI results, t-tests were used to test for significant differences between group means across cycles or between Muskoka and the provincial average. Significant differences in vulnerability were calculated based on the critical difference, which measures the amount of change between samples or populations that is considered meaningful based on the size of the populations sampled.


Participation in the EDI is not universal across Ontario school board and political boundaries, and therefore the provincial average may not be broadly representative of the total Ontario population. For example, Simcoe County did not participate in Cycle 3 of the Ontario EDI. Further, as summarized data is provided to the health unit it can be difficult to compare the results for Simcoe County and the District of Muskoka as the summarized data may reflect different types of analyses. 

The data provided to the health unit excludes special needs children, across Ontario as a whole, special needs students, either observed or reported via parents or medical diagnosis, represented nearly 12% of the sampled children. Not having information about special needs children in Simcoe and Muskoka create barriers to identifying their unique vulnerabilities and challenges. EDI results from aboriginal children are also excluded from the data provided to the health unit. Children attending private schools for senior kindergarten, or who are not enrolled in senior kindergarten are not included in the EDI assessment.

While research has shown that the EDI is a reliable and valid tool for measuring early childhood developmental health, it is subject to the individual interpretation of the teachers administering the survey and how well the teacher knows the student. Children are only included in the EDI if they have been in the classroom for more than a month, however, the length and quality of knowledge a teacher has may influence their assessment.  Training on the use of the EDI instrument is provided to help avoid this bias.

Further, the EDI provides a snapshot of child development and readiness for school, while patterns may emerge in the EDI results, it cannot be used to determine causal associations.