Yeah, I'm gonna talk about math. Go watch t.v. or something until I'm done. (But I'm going to be talking sort of philosophical-like, not all math-like... at least that's the plan.)
So imagine you're 12 or 13, in 7th grade, and have no idea how to do the following:
1. Recall many basic math facts, such a 7 + 8 or 6 * 7.
2. Write an equivalent fraction (and most of the mini-steps that entails).
3. Long division--or, any working algorithm for figuring out what 3,527 divided by 42 is.
4. Hear the word "fraction" without figuratively wetting yourself in fear.
5. Add, subtract, multiply, and divide decimals or fractions.
6. Use a simple formula and given information to find the area of a shape.
7. Multiply a number by a two- or three-digit number.
Some of that is pre-4th grade. Some of that is 6th grade. But remember, in this imagining, you're in 7th grade.
Now, remembering you're in 7th grade, how concerned are you? Or, try this one: how concerned are you willing to appear in front of your peers?
All that in mind, how are you going to be taught how to add, subtract, multiply, and divide integers when you can't figure out to at least count on your fingers when confronted with a problem like "What's 8 plus 7?"
How are you going to work with ratios and proportions when they look like fractions, and fractions freakin' own you?
Now, I know many people who are way older than 12 or 13 and came across at least three things on that list they themselves cannot do. And that's fine, because if you're way older than 12 or 13, odds are you don't have Algebra I, Geometry, Algebra II, and whatever math you're required to take in college coming at you any time in the foreseeable future. I'm perfectly okay with your ignorance in the area of math--as long as you're perfectly okay with my ignorance in the multitude of areas where I'm ignorant.
So now imagine you're the teacher who has to try to get these 7th grade students as close to grade-level as you can before they move on.
It's a lot like trying to scoop the water out of your canoe with a strainer while you're heading toward the waterfall.
At some point every year you have to decide it's time to cut your losses and just teach them as much as you can and hope someone comes along fills in the gaps later.
They're probably not going to. I don't want to ruin the ending for anyone, but it's true.
The good news is a lot of them won't need Algebra and Geometry in their day-to-day life, so once they're through, they can just always make sure they have a calculator at all times and be really good at converting fractions to decimals and vice-versa should they work in any area that requires measuring and calculating with those measurements.
The bad news is they could have gone a lot further and been who knows what if we just could have gotten the job done.