Why Does My Child Need to Know It Before School Teaches It? A Teacher Explains the “Prerequisite” Problem
“Mom, this is stupid.”
I looked up from the stove. My daughter, in seventh grade, was sitting at the kitchen table with her math homework spread out like a crime scene. She pointed to the worksheet. “We’re supposed to ‘recall and use the relationship between fractions, decimals, and percents.’ She hasn’t taught us that yet. How are we supposed to know it?”
I read the top of the page. It was the first assignment in a new unit, and it had one of those “skills check” boxes that textbooks love. The directions said, “Use what you already know about fractions, decimals, and percents to complete the table.”
To her, it felt unfair. And I understood why. From a kid’s perspective, school is supposed to be the place where you learn things. If you already had to know the material before the lesson, what exactly was the teacher doing?
But I’d also been a teacher long enough to know the uncomfortable truth: in most subjects, learning doesn’t work the way kids think it does. It’s not a straight line where the teacher hands you a new idea, you hold it for a day, and then you move on. It’s more like building a wall. You can’t lay a brick in the middle of the air. The bricks below it have to be dry and in place first. If they’re not, the whole thing wobbles.
That’s what those “you should already know this” assignments are checking for. Not whether you’re a genius. Not whether your teacher is lazy. They’re checking to see if the wall is solid enough to hold the next row.
The problem is that nobody explains that to kids. Or to parents, for that matter. So when a child brings home a worksheet that asks questions they haven’t been “taught yet,” it looks like bad teaching. It can feel like the school is saying, “You should have learned this somewhere else, and I’m not going to help you.”
That’s not what’s happening. Or at least, it shouldn’t be.
Let me back up.
When my daughter was in fifth grade, she had a teacher who used to start every new unit with something she called “a warm-up.” It was just two or three questions on the board that reviewed the previous year’s material. Some kids rolled their eyes. They wanted to get to the new stuff. But the teacher said the same thing over and over: “A new idea only makes sense if your brain has somewhere to put it.”
She was right. In education, that “somewhere” is called prior knowledge. It’s the stuff you already know that the new stuff can hook onto. If you’ve never heard of a denominator, then a lesson on adding fractions isn’t just hard. It’s almost meaningless. The teacher might as well be speaking a different language.
That’s why schools do those “advance” assignments. They’re not trying to get kids to teach themselves the whole unit. They’re trying to wake up the parts of the brain that will be needed during the actual lesson.
Take that fractions worksheet my daughter was complaining about. The lesson the next day was going to be about converting fractions to decimals. To follow along, she needed to know that the bottom number of a fraction tells you the total number of equal parts, and the top number tells you how many parts you’re talking about. She needed to know that “percent” just means “out of one hundred.” Those aren’t the new ideas. They’re the old ideas. But if they’re not fresh in her mind, the new idea won’t land.
I tried to explain this to her that night, but she wasn’t buying it.
“So I just have to know it before I learn it?” she asked.
“Not know it like an expert,” I said. “Just know enough to recognize it. Think of it like hearing a song in the car. If you’ve never heard the chorus before, you don’t notice it. But if you’ve heard it once or twice, you can hum along by the second time.”
She frowned. “That doesn’t make sense.”
But it did, which was the problem. The brain works that way. It learns new things by connecting them to old things. If you don’t have any old things to connect to, you have to stop and create them first. And that takes time the lesson doesn’t give you.
That’s the real reason your child sometimes seems lost even though the teacher just explained something clearly. It’s not that your child is slow. It’s that the lesson was built on a foundation that was never put in place, or was put in place so long ago that it crumbled.
So what do you do about it?
The first thing I learned as a parent is that you don’t have to wait for the school to send home a “skills check” to know this is coming. You can do a simple version of it the week before a new unit starts. Most teachers will tell you what’s next, either in a newsletter or a syllabus. When you know a new chapter is coming, sit down with your child the night before, not to teach the material, but just to ask, “What do you already know about this?” Have them flip through the textbook pages. Look at the pictures. Read the new vocabulary words out loud. Don’t worry if they can’t do the problems. You’re not trying to get ahead. You’re trying to get familiar.
Another thing that works is a quick “memory search” for old terms. If the unit is about fractions, ask your child to write down anything they remember about fractions. Even if they’re wrong, it helps. When they say, “The bottom number is the denominator,” and you say “yes, and what does it tell you?” you’ve just put a hook in the wall. The lesson tomorrow can hang on it.
You can also use the “three questions” trick. Before a lesson, your child makes three guesses or questions about the new topic. It doesn’t matter if they’re accurate. “What does percent mean?” “Why do we divide by a hundred?” “Are decimals and fractions the same thing?” That primes the brain. It tells it, “Hey, we’re going to need you to pay attention to this, because we noticed we don’t know it.”
The hardest part for me was fighting my own instinct to fix the gap immediately. When my daughter couldn’t remember what a denominator was, I wanted to sit down and give her a full math lesson right then and there. But you don’t need to do that. In fact, it can make things worse. The goal is to make the child aware of what they don’t know, not to make them feel bad about it. A quick note on a sticky note — “denominator = bottom, tells how many equal parts” — is plenty. She can bring it to class and look at it during the lesson.
There’s also something useful in just being honest with your child about why school feels this way sometimes. You can say, “Your teacher is like a tour guide. She can show you all the rooms in the house, but you have to walk through the hallway yourself. The hallway is the stuff you learned last year. If you skipped it, you need to walk back and get it. It’s not a punishment to go back. It’s just how walking works.”
That analogy actually helped my daughter more than any of my education jargon.
We didn’t solve her fractions problem that night. We made a flash card, and she took it to school the next day. I got an email from her teacher later that week saying she was doing okay, not great, but okay. I think she still grumbles about “stuff you’re supposed to know already.” To be honest, I get it. A lot of it does feel unfair. And sometimes it is unfair, because kids forget, and curricula don’t leave room for forgetting.
But I’ve also seen what happens when a child walks into a lesson already having the quiet little pieces of background knowledge in place. The teacher says, “Remember when we learned about tenths?” and the child nods instead of panicking. That’s not cheating. That’s not a shortcut. That’s just giving your brain a fair chance to learn what it’s supposed to learn.
The school’s job is to teach the new stuff. Your job is to make sure there’s somewhere for it to land. That doesn’t mean we succeed every time. Some lessons go sideways no matter how prepared everyone is. But when I see a “what you should already know” sheet now, I don’t read it as a trap. I read it as a quiet reminder that learning is never really about the one day in class. It’s about all the days before.
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