Red Light, Yellow Light
Red Light, Yellow Light is a critical-reading routine in which participants go through a source and mark the points where a claim may not be trustworthy: red for strong warning signs, yellow for milder ones. It comes from the Visible Thinking work of Project Zero at the Harvard Graduate School of Education. The routine trains people to notice where closer scrutiny is needed; it flags issues and leaves resolving them to a later step.
Facilitation script
- 1
Introduce the source and the purpose. Explain red and yellow lights with two or three examples of warning signs and stress that a mark means 'check this'.
5 min - 2
Individual reading and marking, with a short note on the reason for each mark.
12 min - 3
Pairs compare marks and agree their three most important red or yellow points.
5 min - 4
Collect points on the board in two columns and identify red and yellow zones.
8 min - 5
Discuss which warning signs dominate and what that says about how to use this source.
5 min - 6
Choose the items to investigate and assign who checks what.
5 min
Tips
Make clear at the start that a red light means 'look closer' and does not mean 'false'; otherwise the exercise turns into a verdict on the document or its author.
Ask for the reason behind every mark, because the learning lies in recognising the type of warning sign.
If the source was written by someone in the room, agree the routine with them beforehand and have them mark their own text as well.
Common pitfalls
Treating every red mark as proof that the claim is wrong, which leads the group to dismiss a source that may be largely sound
Marking passages without naming the warning sign, so the list becomes a set of dislikes that cannot be followed up
Using the routine on a colleague's draft without warning, which is experienced as a public takedown and damages trust
Stopping at the list and assigning no checks, which leaves the doubtful claims in circulation with a vague sense of suspicion attached
Flagging only claims people disagree with, while similar unsupported claims that suit the group's view pass unmarked
Variations
Remote: share the document in a tool that allows comments or highlights and have people tag passages R or Y, then sort the comments together. Split a long document into sections and give each subgroup one section before pooling results. The routine can also be applied to a meeting, a pitch or a stretch of everyday experience, with people noting red and yellow moments as they occur. Combine it with a method for testing claims, since this routine only identifies what to examine.
Where it fits
When to use it
A team is about to rely on a report, pitch or business case and nobody has read it critically yet
A group needs a shared, low-threshold habit for questioning claims without it feeling like an attack
You want to turn a long document into a short list of points that need verification
A research synthesis mixes findings with the authors' opinions and the team needs to separate them
Participants tend either to accept sources wholesale or to reject them wholesale
When not to use it
You want a quick vote on proposals or a reading of the room; the Traffic Light card method does that and is unrelated to this routine
The claims have already been identified and now need to be tested; use Claim, Support, Question or assumption testing
The source is very short or purely factual, so there is too little to scan
The author is present and has not agreed to a critical reading; use a structured feedback format that includes strengths
The group needs to find risks in its own plan; a premortem is designed for that
Related methods
Frequently asked questions
What is Red Light, Yellow Light?▾
Red Light, Yellow Light is a routine for reading a source critically. Participants mark passages with a red light where there is a strong sign that a claim may be unreliable and a yellow light where the sign is weaker, then collect and discuss the marks. It was developed by Project Zero at the Harvard Graduate School of Education.
What counts as a red light or a yellow light?▾
Typical signs are sweeping generalisations, bold claims without an argument or evidence, evident self-interest of the author, extreme certainty and a lack of relevant expertise. A red light is a strong instance, a yellow light a milder one. The group can add signs that matter in its own field, such as missing sample sizes.
Is Red Light, Yellow Light the same as the Traffic Light method?▾
No. Traffic Light uses red, yellow and green cards so participants can signal agreement or concern about a proposal. Red Light, Yellow Light is a reading and review routine with no green and no voting. It is also unrelated to the children's game Red Light, Green Light.
How long does Red Light, Yellow Light take?▾
Around 20 to 45 minutes depending on the length of the source. Most of the time goes to individual reading and to collecting the marks. For long documents, send the text in advance or divide it between subgroups.
What happens after the red and yellow lights are identified?▾
The routine only shows where scrutiny is needed. Pick the most important flagged items and decide how to check each one, for example by requesting the underlying data, consulting an independent source or testing the assumption. Record who will do this and by when.
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Try it freeMethod descriptions on Workshop Weaver are original content written by our team, based on established facilitation practices. This method was inspired by work from Project Zero, Harvard Graduate School of Education (Visible Thinking).