In a move sure to annoy his adversaries, Mayor Michael Bloomberg is scrambling to firm up plans for 23 more charter schools in the city before the final bell rings on his mayoralty, reports say.

He has the look of a guy trying to nail as much as he can to the floor before his term ends on Dec. 31.

But it's no mystery why he's in such a rush.

Republican Joe Lhota -- a strong charter supporter -- is running a mayoral campaign that has fallen so far behind even his natural constituency is losing heart.

Democrat Bill de Blasio -- who's not in love with charter schools -- has ramped up a mayoral juggernaut that's now approaching warp speed.

Meanwhile, Bloomberg is struggling to preserve as much of his strong education legacy as he can.

De Blasio says he champions a superior education for all 1.1 million of the city's public school students -- not just a select few. A dash of skepticism would be wise.

More charters -- which are public schools untethered from United Federation of Teachers work rules -- could be a strong force in achieving the broad success de Blasio says he wants. Some have longer school days. Some have a longer school year. Some have classes on Saturdays.

Those are some reasons why standardized tests show charters doing best in poor and struggling parts of the city where traditional district schools do worst.

Thousands of New York City parents get it -- which is why the waiting lists for charters stand at more than 53,000 students in the five boroughs.

Lhota and questioners face a big job in tonight's mayoral debate. They must get de Blasio to say why he would charge some charters rent for using public school buildings. They must ask him to explain why city students would be better off taught by teachers constrained by inflexible work rules. They must persuade him to spell out his creative vision for moving the system ahead.

What kind of chancellor would de Blasio choose? How would he challenge his chancellor and measure success? In short: What's on his schedule for the first day of school?