Fractional CMO vs Head of Growth vs Growth Partner: What Scaleups Actually Need at Series A and B
- Laura Derbyshire
- 1 day ago
- 5 min read
Fractional CMO vs Head of Growth
There’s a very specific moment in a scaleup’s life where everyone starts talking slightly faster.
Revenue is up, the team has doubled, Slack is noisy and the marketing team is doing a lot.
And yet, growth feels heavier than it should; it is somehow less elegant and less convincing. The board asks for clarity, people are swamped by dashboards as they multiply and someone eventually says: “We probably need to hire someone senior.”
Cue Google searches like:
Fractional CMO London Series A
Head of Growth scaleup
Do we need a CMO yet?
This post is for that moment.
Because while these roles sound similar, they solve very different problems. And choosing the wrong one at the wrong time is one of the fastest ways to slow a scaleup down.
The real issue isn’t the role. It’s the stage.
Most hiring mistakes at Series A and B aren’t about capability. They’re about context blindness.
What worked at £3m doesn’t behave the same way at £15m, and importantly, what “growth” meant last year isn’t necessarily what it means now. No job title can fix a growth system that’s out of sequence.
Let’s be clear about what each role does and when it makes sense.
The Fractional CMO: very useful, until they’re not
A Fractional CMO is typically engaged part-time (one to three days per week) to provide senior marketing leadership without the commitment of a full-time hire.
At the right moment, this can be a brilliant move.
When a Fractional CMO works well
Early to mid Series A
You have marketing activity, but no senior direction
Execution exists, but prioritisation doesn’t
The board wants clearer reporting and sharper focus
In other words, you need someone to steady the wheel.
Where it starts to creak
A Fractional CMO is still operating inside your existing growth model, so just bear in mind that if the real problem is:
Unclear positioning
Over-reliance on performance
Rising CAC
Fuzzy brand meaning
A sense that growth has fundamentally changed
…then optimising the current system won’t fix it, and at this point you might be expecting too much from a standard-level Fractional CMO, and you may well be disappointed.
The Head of Growth: brilliant at speed, not at definition
A Head of Growth is typically full-time, deeply embedded, and highly execution-focused.
They are excellent at:
Acquisition
Experimentation
Funnel optimisation
Performance velocity
When a Head of Growth works
Product-market fit is clear
Positioning is settled
Demand already exists
The brief is: “Scale this efficiently”
Where it goes wrong
Heads of Growth are often hired too early or to solve the wrong problem. They can accelerate growth, but in most cases, they cannot define what growth should be.
If demand creation is the real issue, or if brand and category are unclear, a Head of Growth ends up pushing harder on performance until it stops pushing back (which is a familiar story for many Series B boards).
The Growth Partner
A Growth Partner isn’t a job description you post on LinkedIn; it’s a strategic role that sits above execution, not inside it.
Growth Partners work with founders, CEOs and boards to answer the uncomfortable questions most teams are too busy to ask:
Where are we actually stuck?
What has changed in our growth dynamics?
Which levers matter now, and which ones are distracting us?
Is this a hiring problem, or a clarity problem?
What does “good” look like over the next 12–36 months?
This isn’t about running campaigns, it’s about designing the growth system the business will run on next.
Why does this question always show up at Series B?
There’s a reason this debate flares up between Series A and B, because this tends to be when:
Performance efficiency drops
CAC rises quietly at first, then loudly
Sales cycles stretch
Attribution becomes imaginative
Brand exists, but no one can quite explain it
At this point, “doing more” stops working and what’s needed is clarity through:
Clear positioning
Defined category entry points
Alignment between brand and performance
Confidence about who to hire next
This is where a Growth Partner adds disproportionate value.
So which one do you actually need?
I would suggest that if you’re arguing about roles, you’re probably already feeling the limits of your current growth model.
The way to frame it is rather than to start at the job role level: “Should we hire a Fractional CMO vs Head of Growth?” Switch the thinking to: “Where are we on the scaleup growth journey and what does this stage actually require?”
In my experience, that’s the decision most teams skip and yet it’s the one that makes everything else easier.
You can explore the full Growth Journey Framework here >
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FAQs: Fractional CMO, Head of Growth & Growth Partners
What is the difference between a Fractional CMO and a Head of Growth?
A Fractional CMO provides senior marketing leadership on a part-time basis, often focusing on prioritisation, reporting and alignment. A Head of Growth is typically a full-time, execution-focused role responsible for acquisition and performance optimisation. They solve different problems and suit different growth stages.
When should a scaleup hire a Fractional CMO?
A Fractional CMO is most effective in the early to mid Series A stage, when marketing activity is underway but lacks senior direction. They work well when the growth model is broadly sound but needs sharper focus and leadership.
When does a Head of Growth make sense?
A Head of Growth is best hired when product-market fit and positioning are clear, demand already exists, and the priority is scaling acquisition efficiently. They are not designed to define a growth strategy from scratch.
What is a Growth Partner, and how is it different?
A Growth Partner works at the board and leadership level to help scaleups understand where they are in their growth journey, what is constraining growth, and which levers matter most next. Unlike operational roles, they focus on growth clarity, sequencing and long-term value creation.
Do Series A and Series B companies need a CMO?
Not always. Many scaleups hire too early or too late. The right leadership model depends on growth stage, clarity of positioning, and whether the business needs execution or strategic realignment.
Why do scaleups struggle with growth after Series A?
Growth often becomes harder because performance marketing becomes less efficient, CAC rises, and demand creation hasn’t been built early enough. Without brand clarity and strategic alignment, teams end up pushing harder on the same levers.
Is a Growth Partner a replacement for a Fractional CMO or Head of Growth?
No. A Growth Partner doesn’t replace execution roles; they help leadership teams decide which roles are needed, when to hire them, and how to set them up for success.
How do boards decide which growth role is right?
Boards should start by diagnosing the company’s growth stage and constraints. Without that clarity, hiring decisions tend to add complexity rather than momentum.
How does OSER support scaleups making this decision?
OSER works with founders, CEOs and boards to diagnose growth stage, clarify positioning, align brand and performance strategy, and guide leadership hiring decisions. The focus is on building sustainable growth systems, not short-term fixes. We understand all three models, and we deliberately use Fractional CMO as part of a wider growth system, not as a plug-in fix.
