Further numbers:

Canada wide, total school enrollment (elementary and secondary) has been between 5Mn and 5.7Mn in all school types for the last 20 years, undulating up and down.

Total workers employed by the education industry (codes 61 and 611) over the same period has increased form 981k to 1,393k.

So about 40% more people in the industry for 14% more school age students.

So what's going on here? I can think of a few possible explanations:

1. An increase in part time work. Number of workers go up, but total hours of work go down. Edit: full time has actually been increasing as a percentage. Perhaps just educators are getting a part time squeeze?

2. Education includes post-secondary. Since post-secondary has become a lucrative business, employees are more likely to favour working there for more compensation.

3. Since we've sold the narrative of post-secondary being a workforce gateway, the number of people going to post-secondary schools, poaching educators from grade schools. Related to point 2, this poaching is likely to be effective. (1.5Mn to 2.1Mn over the last 2 decades).

4. Increase in overhead. I assume IT requirements have ballooned, but dated buildings may also increase janitorial requirements.

Even with post-secondary included, total students are only up 20%. Teaching has probably become more efficient with IT and other tools. Administration has certainly become more efficient.

All numbers from Statscan, rounding errors abound.