First Lady Michelle Obama wrote yesterday in US News and World Report that we face a teacher shortage. She laments that up to a third of current teachers could retire in the next four years. The solution, she says, is to embark on an aggressive and multifaceted teacher recruitment campaign.

But here’s an interesting thought: What if a million teachers really did retire in the next four years, and we only replaced half of them? 

Catastrophe? Millions of kids without teachers? Nope. In fact, we’d still have a lower pupil/teacher ratio than we did in 1970. Back then, we had 2 million teachers for 45.5 million students. Today, we have 3.2 million teachers for not quite 50 million students.

For the past 40 years, we’ve added teachers a lot faster than we’ve added students. In fact, we’ve added other staff even faster. As a result, the total staff to student ratio has gone up by nearly 75% since 1970.

There are plenty of critical problems with American education, but a looming crisis in the size of the teaching workforce is not one of them.