Strategy Lab · Education & tutoring

One line is wrong. Find the Mistake: a tutoring-school marketing idea built on one deliberate error

An empty tutoring-school classroom in the afternoon, with desks, notebooks and sun through the blinds. On the whiteboard, six lines solving a limit and a 30-second timer.

No name, no email. Nothing is kept.

Keys 1–6: choose a line · Enter: confirm

The demo didn't load. The description below tells you what you'd have seen.

The demo in words: a teacher solves a limit in six lines, and one line hides a deliberate, common mistake. You have 30 seconds to tap it; a wrong line costs 5 seconds. With "No timer" there is no clock and no penalty.

Find the limit, as x tends to minus infinity, of the square root of 4x squared plus x, over x minus 1.

Line 1: the root of 4x squared plus x equals the root of x squared times 4 plus 1 over x.
Line 2: equals the root of x squared times the root of 4 plus 1 over x.
Line 3: equals x times the root of 4 plus 1 over x.
Line 4: so the fraction equals x times the root of 4 plus 1 over x, over x times 1 minus 1 over x.
Line 5: equals the root of 4 plus 1 over x, over 1 minus 1 over x.
Line 6: tends to the root of 4 over 1, which is 2. So the limit is 2.

The answer: the mistake is on line 3. The square root of x² is the absolute value of x, and as x tends to −∞, x is negative, so it is −x. The limit is −2, not 2.

At a glanceEducation / tutoring schools

How can a tutoring school use a deliberate mistake in its marketing?

Find the Mistake is a tutoring-school marketing mechanism: a teacher solves a national-exam-level problem fast on the board, one line hides a deliberate, common mistake, and students race to comment the line. The first 20 correct answers win a mock-exam seat. Typical range: 50–200 mock-exam sign-ups per season. Mechanism Sprint: 10 working days, from €1,500 plus production.

A Mechanism Sprint is how Netex builds one marketing mechanism like this: designed for your sector, produced and measured in 10 working days, with the automated replies to the messages it brings set up before launch.

Netex — digital engineering studio in Heraklion and the Almyros industrial area.

The teacher solved it fast, like the video a student would watch on their phone. Somewhere in these six lines hides a mistake plenty of people make. Can you see it?

Sector: Education / tutoring schools
Mechanics
Demo engine: Board game
Complexity
Production cost

Decode

How it got you

Find the MistakePlay → Decode → Deploy

Mechanism: Dm · Deliberate mistake
Psychology: When students hunt for the error before seeing the solution, the lesson goes deeper: "productive failure" (Kapur, 2008). Retrieval makes knowledge stick (Roediger & Karpicke, 2006). And the pride of "I caught it" is the thing people send to friends. Kapur (2008), Cognition and Instruction · Roediger & Karpicke (2006), Psychological Science
Platform signal: Watch time: students pause the video to read the board, rewatch it, post the line number in the comments and tag classmates. The answer video the next day brings followers.
Honest range: Watch time 2–3× the account's baseline · 50–200 mock-exam sign-ups per season Typical range for a pilot in a Greek SME · Netex estimate

I want one of these for my brand

Deploy

How we'd build it for you

Who it's forFor secondary-school tutoring centres, language schools and teachers with their own channel.

The teacher solves a national-exam-level problem fast on the board. One line hides a deliberate, common mistake.
"Found it? Comment the line." The first 20 correct answers win a seat at a mock exam.
24 hours later, the answer video explains why the mistake is so common.
One series a week per subject: maths, physics, chemistry, essay writing.
A second layer on Facebook for parents, who are often the ones who decide.

Channels and tech

Channels: TikTok, Reels and Shorts for students · Facebook for parents · an automatic message to winners
Tech: Simple production: a board, a camera, a decent microphone. An automatic message to winners and a seat-booking form.
Complexity: 1/5
Production cost: € · Netex estimate

What to expect, honestly

We don't promise viral. We promise a mechanism you can measure.

Watch time against the account's baseline 2–3×
Mock-exam sign-ups per season 50–200

most likely on a first run · A first run usually lands in the lower half of the range.

Guardrails

Minors under 15 (Greece's digital-consent age, Law 4624/2019): any personal data needs a parent's consent. The demo asks for none.
No AI marking of students. Assessing students is a high-risk area under the EU AI Act.
The wrong solution is never left uncorrected for more than 24 hours, and the video says from the start that it hides a mistake.
A second teacher checks every problem before it goes out. One mistake, not two.
Prizes and contests follow promotion rules. No "tag a friend to enter".

Who did it before us

People love catching a mistake, and "I caught it" shares itself.

Third-party results are mostly self-reported, from award entries and vendors. They show a mechanic can work, not what it will do for you.

Year	Who	What they did	Result
c.2022 · UK	Specsavers "Should've"	Billboards with deliberate "blunders" that people spotted and shared.	191 articles, 17M+ earned reach award-entry figure · Love the Work
2023 · UK	Specsavers "The Misheard Version"	A well-known song with deliberately misheard lyrics.	400 pieces of coverage, 100M+ reach, +19% call-centre volume against forecast self-reported · Contagious source (opens in a new tab)

From marketing to AI

Why there's no AI here.

We could have had a model mark the students' answers. We don't. Assessing students is a high-risk area under the EU AI Act, and automated marking is one of our red lines.

Where AI does help a tutoring school is elsewhere: parents' calls in September, enrolments, reminders. Declared as AI, with a person one step away.

AI marking of students: not here
Parents' calls in September
Enrolments and reminders
A person, one step away

Questions about Find the Mistake

Isn't it risky to publish a wrong solution?

Only if it's left wrong. The video says from the start that it hides a mistake, the wrong solution is never left uncorrected for more than 24 hours, and the answer video the next day explains why the mistake is so common. A second teacher checks every problem: one mistake, not two.

Why doesn't this campaign use AI?

Because assessing students is a high-risk area under the EU AI Act, and automated marking is one of our red lines. The game asks for no name or email and keeps nothing. Where AI does help a tutoring school is elsewhere: parents' calls in September, enrolments and reminders, declared as AI.

Are there rules for students under 15?

Yes. In Greece the age of digital consent is 15 (Law 4624/2019), so any personal data from younger students needs a parent's consent. The game on this page asks for none. Prizes and contests follow promotion rules, with no "tag a friend to enter", and a second layer on Facebook speaks to parents.

What results can a tutoring school expect?

We don't promise viral. The typical range, a Netex estimate, is watch time 2–3× the account's baseline and 50–200 mock-exam sign-ups per season. Students pause to read the board, rewatch, post the line number and tag classmates, and the answer video the next day brings followers.

How long does it take, and what does it cost?

As a Mechanism Sprint it is designed, produced and measured in 10 working days, from €1,500 plus production. Production is in the € tier, under €2,000 by Netex estimate: a board, a camera and a decent microphone, plus an automatic message to winners and a seat-booking form. Complexity is 1 of 5.

Mechanism Sprint

What's the mistake everyone makes in your field?

Mechanism Sprint: designed, produced and measured in 10 working days. From €1,500 plus production.

I want one of these for my brand The whole Strategy Lab

We reply within one working day.

The scenario you just played goes straight into the form.