When high-performing charter schools are a niche player in a city, they can source most of their teachers from teacher pipelines such as Teach For America, TNTP, or residency programs.

When high-performing charter schools achieve significant market share, these pipelines often cannot meet the full human capital needs of these schools – both because of cost (they are expensive) and supply (they draw from a narrow talent pool).

Consider a small urban district of 50,000 students.

A 18:1 teacher ratio equals 2,778 teachers in the system.

A 20% turnover rate means 555 teachers need to be recruited into the system each year.

And this is a low end projection: 15:1 ratio with 25% turnover is probably more likely.

But let’s call it 550.

In a market this size, TFA + TNTP might bring in 250 teachers a year.

That leaves a 300 teacher a year gap.

Where will these teachers come from? Some thoughts:

1. The boutique pipelines expand. TFA and TNTP double in size. This is plausible, especially if there is a lot of local philanthropy in the system.

2. Charter schools pull teacher training in house. They directly partner with local colleges and build up internal training capacity. This is also plausible, especially in markets where CMOs have achieved some level of scale.

3. Training programs partner with local universities. Under this model, 3rd party non-profits partner with undergrad institutions to develop teachers, sometimes even bypassing colleges of education located on the same campus. I know of a couple of pilots that are launching based on this model.

4. Colleges of education become more effective and supply an increased number of high-quality teachers.

In a small urban district, I think options (1) and (3) are most likely to succeed. (2) is a little more difficult because there may not be as many large CMOs that can achieve the economies of scale needed to run an internal program.

In a large urban district, I think options (2) and (3) are most likely to succeed. (1) is little more difficult because TFA and TNTP do not scale as well.

I am skeptical (4) will work at any scale anytime soon.

One last note, it always bothers me when people argue that charter school advocates ignore teacher quality. These critics often point to the fact that countries such as Finland improved their educational systems via better teacher recruiting and development, not via charters and choice.

This may well be true.

But, as far as I can see, in this country the best advancements in teacher recruitment and development are closely aligned with the charter movement.

Of course, I’d love it if traditional education schools were reforming themselves.

But they are not.

For now, at least, the solutions lie elsewhere.