Growth, Retention & Metrics

Welcome. This is a hands-on growth course for founders building Kaern startups. By the end, you'll be able to model your business as a funnel, pick acquisition channels that actually fit your product, design onboarding that turns signups into habitual users, measure and fight churn, build referral loops that compound, and run experiments against a single north-star metric. We'll work from real numbers wherever we can — including stories from cycleX, where we grew from a leaky early funnel to a retention-led engine — so the lessons stay grounded in what really happens, not what looks good on a slide.

Your tutor: I'm Mara. I've spent years in the trenches of early-stage growth — some of it painful, most of it instructive. I teach the way I wish someone had taught me: with analogies you'll remember at 2am, real war stories, and exercises you'll run against your own startup, not a toy case. Bring your real data. We'll get our hands dirty.

How this course works: Six modules, each with teaching scripts, a worked example, a hands-on exercise you do on your own company, common mistakes I see constantly, and quick checks for understanding. We close with a capstone where you build a complete growth model and 30-day experiment plan for your startup, graded against a clear rubric.

Module 1 — The Growth Model & the AARRR Funnel

Learning objectives

• Describe a startup as a system of inputs, conversion rates, and outputs rather than a single "users" number.
• Map your business onto the AARRR funnel (Acquisition, Activation, Retention, Referral, Revenue).
• Identify which stage of your funnel is the binding constraint right now.
• Calculate how a change at one funnel stage propagates to overall growth.

Lesson 1.1 — Growth is a system, not a number

Teaching script. Let's start somewhere uncomfortable: most founders, when I ask "how's growth?", answer with a single number — "we hit 5,000 users." That tells me almost nothing. Imagine a bathtub. Water pours in from the tap, and water drains out the plughole. The water level is your user count. If I only tell you the level is rising, you don't know whether the tap is wide open or the drain is plugged — and those require completely different fixes. At cycleX, early on, we celebrated a rising level for three months before realising the drain was wide open; we were just pouring water faster than it leaked. The moment paid acquisition paused, the tub emptied. Growth is the relationship between inflow and outflow, broken down by stage, not the level itself. When you think in systems, you stop asking "how do we get more users?" and start asking "where is the leak, and what's the cheapest place to plug it?" That single reframe is worth more than any tactic I'll teach you. So here's my question to you: if your startup is a bathtub, do you actually know your drain rate today — or are you only watching the level?

Lesson 1.2 — AARRR: a shared map of the journey

Teaching script. Dave McClure gave us five letters that I still use every single week: AARRR — Acquisition, Activation, Retention, Referral, Revenue. People call it "pirate metrics" because it sounds like a growl, but think of it as a map of one human's journey through your product. Acquisition: they find you. Activation: they have a first great experience — the "aha." Retention: they come back. Referral: they bring a friend. Revenue: they pay. Here's why a shared map matters: without it, your marketer optimises clicks, your designer optimises signups, your support team optimises tickets, and nobody notices that 80% of activated users vanish in week one. The map forces one conversation. At cycleX we drew this funnel on a whiteboard and wrote the real conversion rate next to each arrow. It was humbling — our acquisition was fine, but only 12% of signups ever reached activation. The map didn't fix anything by itself; it just made the leak impossible to ignore, which is exactly what a good map does. Where on this map do you think your biggest drop-off is — and would your co-founder give the same answer?

Worked example

cycleX, simplified monthly funnel:

• Visitors: 20,000
• Signups (Acquisition→Activation entry): 2,000 (10% of visitors)
• Activated (completed first core action): 240 (12% of signups)
• Retained at day 30: 144 (60% of activated)
• Referred a friend: 22 (15% of retained)
• Paying: 86 (60% of retained)

Notice: acquisition looks "fine," but activation (12%) is the binding constraint. Doubling visitors to 40,000 yields ~288 activated. Doubling activation to 24% yields ~480 activated — from the same traffic, at near-zero marginal cost. The math tells you where to spend the next two weeks.

Hands-on exercise

Draw your own AARRR funnel for the last full month. For each of the five stages, write the absolute number and the conversion rate from the previous stage. Then circle the lowest conversion rate. That's your candidate constraint. Write one sentence: "If I improved [stage] from X% to Y%, I'd get ___ more [next-stage users] from the same top-of-funnel."

Common mistakes

1. Reporting the level, not the rates. "We grew 10%" hides whether you grew the tap or unplugged the drain.
2. Optimising a stage that isn't the constraint. Pouring money into ads when activation is broken just makes the leak more expensive.
3. Defining stages vaguely. "Active user" must mean a specific action, or every number downstream is fiction.

Check for understanding

1. In the bathtub analogy, what do the tap and drain represent, and why is the water level misleading?
2. Given the cycleX numbers, which is cheaper — doubling visitors or doubling activation — and why?
3. Write a one-sentence definition of "activated" for your own product. Is it a specific, observable action?