An interesting claim: We have too many teachers

Andrew J. Coulson makes the claim We Have Too Many Teachers Already! He starts with:

----------
A story yesterday on CNNMoney.com describes the plight of Jenny Frank, who is young and eager to begin a career in teaching but hasn’t been able to land a job. It’s always sad to hear of people failing to find work in their chosen field, but the article in question completely misses a staggeringly important national story. As I mentioned this morning on Fox ‘n’ Friends: we have about 1.5 million too many teachers already!
Since 1970, public school enrollment has barely budged–up just 9 percent. Over the same period, employment has doubled. We’ve added 3 million new government school jobs. Half of those are teachers, another quarter are teachers’ aides, and the rest are service personnel and bureaucrats. This hiring binge has contributed to a quadrupling in the real, inflation-adjusted cost of a k-12 education: from $38,000 to $150,000 (constant 2009 dollars). It has not contributed to improved student achievement which, at best, has been flat at the end of high-school over that entire period.
----------

I realize that politically it would be very hard to layoff even a fraction of the surplus teachers we have now.