If Mayor Bloomberg had his druthers, he would fire half the city’s teachers and pay the remaining half more to supervise twice-as-large classes.

That’s what he said during a wide-ranging speech at the Massachusetts Institute of Technology on Tuesday in which he argued that weak training, social change, and the teachers union have conspired to fill New York City’s schools with less-than-ideal teachers.

“If I had the ability, which nobody does really, to just design the system and say, ex cathedra, this is what we’re going to do, you would cut the number of teachers in half, but you would double the compensation of them, and you would weed out all the bad ones and just have good teachers, and double class size with a better teacher is a good deal for the students,” Bloomberg said.

Listen to the portion of the speech where Bloomberg talks schools (starting at about 5:00): 11-29-11 MIT Speech – Part 2

The comments have drawn fire from UFT President Michael Mulgrew, elected officials, and many others. But while they were provocative and unusually specific, the speech tread familiar territory for the mayor.

Bloomberg has long said that he doesn’t see class size as a pressing issue and would opt for better teachers over more teachers. The portion of his speech that dealt with education recycled some of his favored rhetorical flourishes, such as comparing the importance of teacher quality to the value of “location, location, location” in real estate. You can see him make the same analogy in this 2008 video, in which he says about class size, “I don’t even know why the issue comes up anymore.”

And especially under ex-Chancellor Joel Klein, Bloomberg’s Department of Education has pushed the idea that many city teachers are not up to par, launching a sustained push in 2007 to usher more weak teachers out of the system and last year battling against “last in, first out” seniority layoff rules.

Still, Bloomberg’s suggestion of how many city teachers should be sloughed off far outstripped the city’s own estimates. When a new teacher evaluation system was piloted in 20 schools last year, 18 percent of teachers were rated “ineffective” — far higher than the 3 percent given unsatisfactory ratings under the current system, but nowhere near 50 percent.

Less provocative, but perhaps more surprising, was a comment in the speech that signaled a point of disagreement between Bloomberg and Klein, who now heads News Corporation’s digital education unit.

“It may be heresy in this day and age to say so, but there’s not a lot of evidence that when you introduce a lot more technology in the classroom the results are better,” the mayor said, according to DNAInfo. Under Klein’s leadership, the DOE invested heavily in digital learning.

“I’ve always been intrigued by everybody wants to put a computer in every classroom and in front of every kid,” he said, adding that cell phones and iPads are prohibited in city schools over concerns about “the lawsuits over the pornography that the kids would be watching.”