One of the joys of specializing in the ISEE is that I get to identify patterns in how students interact with specific skills and concepts. After working with hundreds of 4th and 5th graders preparing for the Lower Level ISEE, I can confidently predict some of the most common mistakes, especially in the Quantitative Reasoning and Math Achievement sections.

Because so much of the test content is above grade level, students often encounter certain math ideas for the first time. But interestingly, one of the most consistently missed topics isn’t an advanced concept. It’s median.

Median: Deceptively simple

Median is a perfect example of how a “simple” concept can go wrong in many ways, and why it’s imperative to build strong habits around the basics, not just understand them intellectually. Parents and students often assume that once a mistake is made on something like median, it won’t happen again. After all, it’s “easy,” right?

But here’s the truth: if you made the mistake once, you’re very likely to make it again. Understanding the concept isn’t enough to prevent errors. What actually helps is building a habit or strategy around the concept. A step-by-step system that helps students move through the problem without error.

Think of it like putting your keys in the same place every time you walk in the door. If you just intend to remember where you left them, you’ll probably spend a lot of time searching later. But if you have a system (a dish by the door, a hook on the wall), you don’t even have to think about it; you just follow the routine and avoid the chaos.

The same goes for math.

The Most Common Median Mistakes

Here’s what I frequently see when students miss median questions:

Mistake #1: Mixing up mean, median, and mode
Understandable, especially with similar-sounding terms. But even once kids correctly recall that median means “the one in the middle,” they’re often not in the clear.

Mistake #2: Forgetting to put the numbers in order
Students remember that the median is the number in the middle, but they select the number that is visually in the middle of a graph or table without reordering the values from least to greatest first.

Mistake #3: Picking the “middle” number from a list that’s ordered incorrectly
Even when numbers are presented in a list, students sometimes assume they’re already in order (or don’t check carefully), and just grab the one in the center.

Mistake #4: Skipping a number when rewriting the list in order
This one happens all the time. A student knows what to do and begins rewriting the numbers from least to greatest. But they accidentally leave one out, especially when there are several numbers clustered in the same range, like the 20s or 30s. So they end up with only 6 numbers instead of 7, and their “middle” number is wrong.

This is why relying on understanding alone isn’t enough. We need a repeatable method that helps students slow down and double-check their work.

A Simple Habit for Median Problems

Here’s the system I recommend to help students avoid these common errors:

1. Count how many numbers you have.
   Say it out loud or write the total on your paper.
   
2. Draw that number of dash marks or blanks.
   This creates a visual expectation for how many numbers the student needs to write.
   
3. Begin filling in the numbers from least to greatest.
   As you place each number, ask yourself: “Did I already write this one?” and “Are there any others in this range I haven’t added yet?”
   
4. Double-check your list.
   Especially when moving from one range of numbers to another (like from the 20s to the 30s), pause to scan the original list again to make sure they’re all there.
   

There’s nothing wrong with needing a system for something “simple.” In fact, that’s what strong test-takers do: they rely on habits, not just memory. So the next time your child misses a median question, help them build a better routine. That’s what sets them up for real confidence on test day.

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• ISEE