Just for fun, I have selected a random reading comprehension sample from the net to see just how much core knowledge is required for real understanding. The test is aimed at students on the fourth grade level.
How many things can you see in the night sky? A lot! On a clear night you might see the Moon, some planets, and thousands of sparkling stars.
You can see even more with a telescope. You might see stars where before you only saw dark space. You might see that many stars look larger than others. You might see that some stars that look white are really red or blue. With bigger and bigger telescopes you can see more and more objects in the sky. And you can see those objects in more and more detail.
But scientists believe there are some things in the sky that we will never see. We won't see them with the biggest telescope in the world, on the clearest night of the year.
You might find it hard to imagine that stars die. After all, our Sun is a star. Year after year we see it up in the sky, burning brightly, giving us heat and light. The Sun certainly doesn't seem to be getting old or weak. But stars do burn out and die after billions of years.
As a star's gases burn, they give off light and heat. But when the gas runs out, the star stops burning and begins to die.
As the star cools, the outer layers of the star pull in toward the center. The star squashes into a smaller and smaller ball. If the star was very small, the star ends up as a cold, dark ball called a black dwarf. If the star was very big, it keeps squashing inward until it's packed together tighter than anything in the universe.
Imagine if the Earth were crushed until it was the size of a tiny marble. That's how tightly this dead star, a black hole, is packed. What pulls the star in toward its center with such power? It's the same force that pulls you down when you jump — the force called gravity. A black hole is so tightly packed that its gravity sucks in everything — even light. The light from a black hole can never come back to your eyes. That's why you see nothing but blackness.
So the next time you stare up at the night sky, remember: there's more in the sky than meets the eye! Scattered in the silent darkness are black holes — the great mystery of space that's because they're invisible. They're the mysterious dead stars called black holes.
- I can certainly see how this would be an intriguing passage for a fourth grader, but there is a lot that the author has assumed. For example, the reader must know what the difference is between the Moon, planets, and stars. Although context clues such as "the" instead of "a" and the capitalization of "Moon" might be enough to suggest that Earth has only one natural satellite, I suspect that this fact needs to be understood ahead of time.
- The fact that these things are visible each night requires an understanding of periodicity, if not necessarily rotation. The student must know that a telescope somehow magnifies images, and that the larger the telescope is, the more powerful its magnification.
- They must have an understanding of scale as it pertains to the decimal system of measurement. "Billions" is a lot of years, more than most adults can conceive of, let alone a child.
- There needs to be knowledge of the three common phases of matter, as well as chemical combustion. (Although it should be noted here that the flammability of certain gases in our atmosphere has nothing to do with the nuclear reactor of the sun. I don't know if the author is ignorant or finds it easier to massage certain key facts.)
- Students also need to understand gravity. They need to know that it is often related to the size of objects, which for the purposes of this paragraph, serves as an indirect measure of mass.