Swerdlow Improvement Partners

Resources · Continuous improvement

The pebble problem

A rapid improvement cycle picks what to work on by irritation. The outcome it is meant to move is chosen by accountability. Those are two different selection rules, and they do not always point at the same thing.

Two rules, four boxes

Where would your team put it?

  1. Pick a problem: the pebble or the constraint.
  2. Select the box where you think your team would put it.
  3. See where it belongs and what happened one cycle later.
  4. Try the other problem.

The pebble

Intake requires the same case details to be typed into two systems. Every worker mentions it. It is real, persistent, and fixable.

One cycle later

Twenty minutes saved per case, morale up, the measure moves. See the research

The constraint

Referrals sit in a provider queue for three weeks before anyone is contacted. No one complains, because the delay happens somewhere no one on the team can watch.

One cycle later

Untouched, and it is the reason families wait. See the research

How much it moves the outcome ↑
Staff often feel it · moves the outcome

The real wins

Felt by staff and load bearing for the outcome. Rare, and worth the whole method when it happens.

Staff seldom feel it · does not move the outcome

Leave it

Nobody minds and nothing turns on it.

Staff often feel it · does not move the outcome

The busy quadrant

Everyone is working, the measures improve, and the outcome does not move. This is where pebbles cluster.

How much staff feel it →

Illustration, not an example from the article. It is here to show the shape of the problem, and the same shape appears anywhere a team improves what it can see.

The cadence is the pressure. Short cycles reward problems that produce a visible win in weeks. Outcome change takes quarters. So the tempo that keeps teams learning also pulls them to the right and down, toward what is felt and away from what is load bearing. That is not a flaw in the method. It is the thing the method has to be designed against. See the research

When what staff feel is a fair guide

The pebble rule is not a mistake, and it is not only about morale. Selecting purely from above often produces improvement work that staff do not take up, so participation is a real constraint and starting from what people feel is how you buy it. See the research What staff feel also genuinely tracks what moves the outcome under three conditions, and they are worth checking rather than assuming.

The staff experience is on the causal path.

In teaching, casework and coaching, the worker’s time and attention is the active ingredient. Friction that burns worker time is then doing real damage to the outcome, not just to the day. See the research

Turnover is the binding constraint.

Where the system loses people faster than it can replace them, morale stops being a side effect and becomes the mechanism. See the research

The system is young.

Early on, the obvious problems really are the big ones. That stops being true once a few rounds of the obvious have been fixed.

The seam

The small but persistent challenges affecting staff or outcomes.
Matthew Stagner, NORC at the University of Chicago, on how to choose what to test first

Staff and outcomes are two different ways of picking a problem, and the definition holds them together with an or. When the two point the same way, the cycle is doing exactly what it promises. The design question is what a team does on the days when they do not.

When I asked him about this line, Matthew Stagner said staff issues can be the pathway to outcomes not being achieved. A team that picks a pathway, counts it, and reports the count is still on the staff side.

I wrote about a time this happened in my own work: the team and the count, and the box that stayed empty. To try it on your own last cycle, use the look-back grid.

Drawn from “Programs Need Continuous Learning, Not Just Evaluation,” Matthew Stagner, NORC at the University of Chicago, September 2026. The quoted phrase is his. The quadrants, the example and the reading of the seam are mine.

What the research says

Open a line to see the research behind it.

Short cycles have to be designed with care.

Reed and Card argue that “the problem with PDSA is the oversimplification of the method as it has been translated into healthcare and the failure to invest in a rigorous and tailored application of the approach.”

  • Reed, J. E., & Card, A. J. (2016). The problem with Plan-Do-Study-Act cycles. BMJ Quality & Safety, 25(3), 147–152. Source
The problems that come up most may not be the ones that matter most.

Tversky and Kahneman showed that people judge how frequent or likely something is by how easily examples come to mind, which they called the availability heuristic. A problem no one on the team can watch does not come to mind, however much it moves the outcome.

  • Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology, 5(2), 207–232. Source
A measure can improve while the outcome stays put.

Campbell warned that “the more any quantitative social indicator is used for social decisionmaking, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor.” The busy quadrant is where that shows up.

  • Campbell, D. T. (1979). Assessing the impact of planned social change. Evaluation and Program Planning, 2(1), 67–90. Source
Shared decisions lead to better implementation.

Durlak and DuPre’s review found that shared decision-making among providers, administrators, researchers, and community members “has consistently led to better implementation,” and that providers who recognize a specific need for a change are more likely to carry it out.

  • Durlak, J. A., & DuPre, E. P. (2008). Implementation matters: A review of research on the influence of implementation on program outcomes and the factors affecting implementation. American Journal of Community Psychology, 41(3–4), 327–350. Source
Teachers are the school factor that matters most.

RAND summarizes the research this way: “teachers matter more to student achievement than any other aspect of schooling.”

  • RAND Corporation. (2012, October 3). How should we measure teacher effectiveness? Source
Teacher turnover lowers achievement.

Ronfeldt, Loeb, and Wyckoff studied more than 850,000 New York City fourth- and fifth-grade student observations over eight years. Students in grade levels with higher teacher turnover scored lower in both English language arts and math, and the results point to a disruptive effect of turnover beyond changes in teacher quality.

  • Ronfeldt, M., Loeb, S., & Wyckoff, J. (2013). How teacher turnover harms student achievement. American Educational Research Journal, 50(1), 4–36. Source

This tool can also run as a full-day session with your team. See ways to work together.

If your team is deciding what to work on next, I would love to hear about it.

Send a short note about the program or question and the decision you are facing.

I read every note myself and reply within the week.