You gotta love the way APTA cherry picks their dates to exaggerate the growth in ridership. Transit ridership in 1995 was the lowest since 1978. Comparing growth from the lowest point over the past 30 years to the second highest point isn’t going to give you a reliable indicator of the long-term trend. Over the past decade (that is, since 1999), ridership has grown only about 11%. Over the past two decades (since 1989), ridership has grown only about 14%. Population has grown faster.

And most of the ridership growth over the past decade or so is accounted for by heavy rail in just a few big cities, mainly New York. These cities have large populations of transit-dependent, low-income immigrants. The recent growth is largely an artifact of immigration, not a shift in preferences or behavior among the population in general.

As for light rail, ridership may have grown over the past year in nine cities, but it fell in seventeen cities. Overall, light rail ridership fell by half a per cent, despite significant growth in capacity.

The details:
585,000 students taking 2.2 trips a day for 170 school days totals about 221 million trips per year. Divide 221 M by 10,200 million national transit trips results in approximately 2.1 percent of trips.
The percent of NYC students of daily transit trips would be higher if only school days were being compared.

Student ridership data: http://www.streetsblog.org/2010/03/01/the-truth-about-student-fares-mta-a-huge-bargain-for-state-and-city/

If NYC total daily transit ridership is around 8 million (quick guess??) and school trips are about 1.3 million a day, then MTA public school student ridership is about 16% of all trips.
But who’s counting.
According to our elected officials “It don’t mean nothing, anyway.”
And we don’t have to pay for nothing, do we?

note: I will take as least as much responsibility for any math errors in the above calculations as our elected officials take for the accuracy of their state, school and MTA budgets. Anything above zero is more responsible.