Most of what goes wrong after a merger is cultural and nobody catches it for eighteen months, by which point the key talent has quietly left and the synergy case has quietly been rewritten. The conventional advice is "run town halls and listen". The advice is not wrong but it is not enough. Structured assessment, used early, lets you see the friction before it becomes attrition.
The 90-day shape
Assume a deal that has closed, both companies still branded separately, integration sponsor named, HR Director on the acquiring side leading the people workstream. The sequence below assumes 200-1,500 people each side.
Day 0 — 30: Culture Preferences across both populations
Run a Culture Preferences assessment across a representative cross-section of each company — ideally all of leadership, plus a stratified sample of the rest. The output is a map of how each organisation thinks about things like:
- Pace of decision-making (fast-and-iterate versus considered-and-committed).
- Hierarchy (flat and self-directed versus structured and role-defined).
- Conflict (direct and open versus indirect and private).
- Risk (optimistic and experimental versus cautious and analytical).
Two companies that look similar from the outside often have large gaps on these dimensions. The gap is not the problem; the gap not being named is the problem. The first deliverable of the integration is a one-page visual of where each culture sits on each axis, shared openly with the leadership of both sides.
Day 30 — 60: Work Values for the combined leadership
The Culture map tells you about the organisations. The Work Values map tells you about the individual leaders who now have to work together. Run Work Values across the combined top two layers — call it the top 40-80 people.
What you are looking for: pairs of counterpart leaders (an acquiring-side function head and an acquired-side function head, for instance) whose values are diametrically opposed. Achievement-versus-Collaboration is a common collision. Autonomy-versus-Security is another. These are the pairs most likely to break the integration in the first six months.
The intervention is simple: pair the leaders, let them see each other's reports, book a ninety-minute facilitated conversation. The aim is not agreement; it is predictability. Each leader leaves knowing which decisions the other will find easy and which they will find hard, and what to ask for help with.
Day 60 — 90: Conflict Style at the interfaces
By day 60 you have surfaced the cultural gaps and the leadership values collisions. Now you need to know how the two sides fight, because they will. The Conflict Style assessment splits people across five archetypes — Competing, Collaborating, Compromising, Avoiding, Accommodating — and maps their defaults under pressure.
Run this at the team interfaces: the handover points, the joint committees, the places where work has to flow across the old boundary. Two high-Avoiding teams will quietly lose momentum without anyone noticing. A high-Competing acquiring team next to a high-Accommodating acquired team will produce an apparent consensus that masks real dissent; the acquired team will leave.
The mistake integration sponsors make
They run engagement surveys instead of culture assessments. Engagement surveys tell you how people feel. Culture assessments tell you how people behave. In the first 90 days of an integration, how people feel is noisy — the result of announcements, rumours, HR comms, sleep deprivation. How people behave is signal. Buy the signal.
The mistake HR Directors make
They run the assessments but keep the results inside HR, releasing only "summaries" to leadership. This is a mistake of protection disguised as professionalism. Share the actual reports. Leaders who see their counterpart's Work Values profile will have a better first conversation than leaders who are told "you and Jane have some differences in approach". The specificity earns trust; the summary does not.
When to bring external facilitation
For the Work Values pair-conversations: always, if either side is above 500 people. The conversations work better when the facilitator is not somebody either party will see again in the corridor. For the Culture Preferences debrief: optional; a well-prepared internal HRD can run it.
A note on consent
Every person in this sequence should have consented to their report being shared with their counterpart. In most jurisdictions this is a legal requirement, and in all jurisdictions it is the right thing to do. Build a consent step into the assessment invitation. The small number of people who decline should be honoured — and you will learn something useful about what they are nervous about.