It sounds like you’re teasing a classic math hack! There are a few famous “old tricks” that fit that description perfectly, depending on what age group you’re teaching.

Here are the top three legendary methods that usually make multiplication click for kids instantly:

1. The Japanese Multiplication Method (Visual Lines)

This is a massive hit for visual learners. Instead of memorizing numbers, kids just draw lines and count the intersections.

How it works for $21 \times 13$:

• Draw 2 parallel lines diagonally, leave a space, then draw 1 line (representing 21).
• Draw 1 line crossing them the other way, leave a space, then draw 3 lines (representing 13).
• Count the places where the lines cross in the left corner, the middle corners (added together), and the right corner.
• Boom—you get your answer visually!

2. The 9s Times Table “Finger Hack”

If a child is struggling specifically with their 9s, this physical trick feels like magic and takes five seconds to learn.

How it works:

• Hold out both hands in front of you, fingers spread.
• To do $9 \times 4$, fold down your 4th finger (from left to right).
• Look at your hands: You have 3 fingers standing to the left of the folded finger, and 6 fingers standing to the right.
• Put them together: 36!

3. The “Skip Counting” Dance or Song

For younger kids just starting out, treating multiplication as glorified skip counting is the ultimate shortcut. Turning the 3s, 4s, or 7s into a rhythmic chant or song (like singing the 3s to the tune of “Jingle Bells”: 3, 6, 9, 12, 15, 18…) removes the anxiety of “math” and taps into audio memory.

Which specific trick were you thinking of, or were you about to share a different hidden gem?