Answer: This is one of those questions Google asks just to see if the applicant can explain the key challenge to solving the problem.
Reader Matt Beuchamp came up with a dandy answer, writing:
I figure a standard school bus is about 8ft wide by 6ft high by 20 feet long - this is just a guess based on the thousands of hours I have been trapped behind school buses while traffic in all directions is stopped.
That means 960 cubic feet and since there are 1728 cubic inches in a cubit foot, that means about 1.6 million cubic inches.
I calculate the volume of a golf ball to be about 2.5 cubic inches (4/3 * pi * .85) as .85 inches is the radius of a golf ball.
Divide that 2.5 cubic inches into 1.6 million and you come up with 660,000 golf balls. However, since there are seats and crap in there taking up space and also since the spherical shape of a golf ball means there will be considerable empty space between them when stacked, I'll round down to 500,000 golf balls.
Which sounds ludicrous. I would have spitballed no more than 100k. But I stand by my math.
Of course, if we are talking about the kind of bus that George Bush went to school on or Barney Frank rides to work every day, it would be half that....or 250,000 golf balls.