ESSA's "Promising" evidence designation (Tier III) is one of the most common evidence claims school leaders encounter when evaluating literacy programs. Understanding exactly what that label means, and what it doesn't, can help schools make more informed purchasing decisions.
ESSA Tier III evidence requires at least one well-designed and well-implemented correlational study that statistically controls for selection bias and shows a statistically significant, positive effect on a relevant student outcome. It is a lower bar than the experimental (Tier I) and quasi-experimental (Tier II) studies above it because a correlational study shows a relationship rather than proving cause.
What Tier III requires, precisely
Of the four ESSA evidence tiers, Tier III, "Promising," is the one many curriculum claims rest on, and the one most often misunderstood. Its requirements are specific. To meet Tier III, a program needs at least one study that is correlational in design, that includes statistical controls for selection bias, that is well-designed and well-implemented by the Department of Education's standards, and that found a statistically significant and positive effect on a relevant outcome. If any one of those pieces is missing, the program does not meet the Tier III standard.
Two of those requirements do most of the work. The "statistically significant and positive effect" rules out studies that found nothing, or found harm. The "statistical controls for selection bias" is what separates a real Tier III study from a simple before-and-after chart, because it is an attempt to account for the possibility that the schools using the program were already different from those that were not.
The study-design ladder
The three highest ESSA tiers are defined by the kind of study behind them, and the difference between them is really a difference in how confidently you can say the program caused the result.
| Study design | ESSA tier | What it does | Causal claim |
|---|---|---|---|
| Experimental (randomized controlled trial) | Tier I (Strong) | Randomly assigns students or schools to the program or a comparison group | Strongest: supports that the program caused the result |
| Quasi-experimental (matched) | Tier II (Moderate) | Compares a program group to a similar comparison group that was not randomly assigned | Moderate |
| Correlational, with controls | Tier III (Promising) | Examines the relationship between using the program and outcomes, controlling statistically for selection bias | Weakest of the three: shows a relationship, not cause |
Random assignment is what makes an experimental study so strong: because students or schools are assigned to the program by chance, the groups are comparable to begin with, so a difference in outcomes can be attributed to the program. A quasi-experimental study mimics this with a carefully matched comparison group but cannot fully rule out that the groups differed in some hidden way. A correlational study, the Tier III standard, simply looks at whether using the program is associated with better outcomes, then uses statistics to control for known sources of bias.
Why correlational evidence is "promising," not "strong"
The honest reason Tier III sits where it does is the oldest caution in research: correlation is not causation. A correlational study can show that schools using a program tend to have better reading scores, and the statistical controls can reduce the chance that the result is an artifact of which schools chose the program. But controls can only adjust for factors the researchers measured and anticipated. They cannot guarantee that something unmeasured, a more motivated staff, a wealthier community, a simultaneous initiative, is not the real cause.
That is why Tier III is genuinely useful and genuinely limited. It is meaningful evidence, enough to qualify a program as "promising" and to count for school-improvement funding. It is not proof that the program will produce the same result in your schools.
For school leaders, the question is rarely whether Tier III evidence is "good enough." The better question is whether the evidence provides the level of confidence you need for the decision you are making. A districtwide curriculum adoption, for example, may warrant stronger evidence than a smaller pilot or targeted intervention. Understanding what Tier III does, and does not, tell you helps you weigh those decisions more thoughtfully.
What to check in a vendor's Tier III claim
Because Tier III is the most attainable of the top three tiers, it is also the evidence level schools are most likely to encounter in curriculum and professional learning materials. That makes it especially important to understand what the designation does, and does not, mean. A handful of questions separate a sound claim from a hopeful one.
Is there an actual study, and is it correlational with controls for selection bias? A logic model, a testimonial, or a satisfaction survey is not a Tier III study. If a publisher or provider cannot point to a correlational study with statistical controls, the claim is not Tier III, whatever the brochure says.
Did the study find a statistically significant, positive effect? This is a requirement, not a detail. A study that found no significant effect does not establish Tier III, and "we have a study" is not the same as "we have a study that worked."
Is the study on the product you are buying, and the population you serve? Evidence for a prior edition, a different grade band, or a very different student population does not automatically carry over.
Does it meet What Works Clearinghouse standards? That is the bar the Department of Education uses for "well-designed and well-implemented." Independent sources such as the WWC or the Evidence for ESSA database can confirm a rating rather than leaving you to trust the vendor's own label.
Does Tier III qualify for funding?
Yes, and this is often the practical reason the question comes up. Tier III is the floor for the most restrictive common requirement: interventions funded under Section 1003 school improvement must meet Tier I, II, or III. So a genuine Promising-evidence program qualifies for those funds, while a Tier IV "demonstrates a rationale" program does not. (The full breakdown of which tiers your funding requires is here.)
The bottom line
Tier III evidence is meaningful evidence, but it should be understood for what it is. A program with Promising evidence has research supporting a positive relationship with student outcomes, but it has not been tested with the same level of causal confidence as Tier I or Tier II. Knowing that distinction helps schools ask better questions, compare programs more thoughtfully, and make evidence-informed decisions rather than relying on marketing labels alone.
Frequently asked questions
What is ESSA Tier III (Promising) evidence?
Tier III, or Promising evidence, requires at least one well-designed and well-implemented correlational study that statistically controls for selection bias and shows a statistically significant, positive effect on a relevant outcome. It is the third level in ESSA's four-tier framework, below Strong (Tier I) and Moderate (Tier II).
What kind of study qualifies for ESSA Tier III?
A correlational study that includes statistical controls for selection bias, meets the Department of Education's standard for being well-designed and well-implemented, and finds a statistically significant, positive effect. A study without controls for selection bias, or one that found no significant effect, does not qualify.
What's the difference between correlational, quasi-experimental, and experimental studies?
An experimental study (Tier I) randomly assigns participants to the program or a comparison group, supporting the strongest causal claim. A quasi-experimental study (Tier II) uses a matched comparison group without random assignment. A correlational study (Tier III) examines the relationship between using a program and outcomes, controlling for bias, but shows association rather than cause.
Does ESSA Tier III evidence qualify for school improvement funding?
Yes. Interventions funded under Section 1003 school improvement must meet Tier I, II, or III, so a program with genuine Promising evidence qualifies. Tier IV, which rests on a rationale rather than a study, does not qualify for those funds.
How do I check a vendor's Tier III claim?
Confirm there is a correlational study with controls for selection bias, that it found a statistically significant positive effect, and that it is on the product and population you are buying for. Verify the rating through an independent source such as the What Works Clearinghouse or Evidence for ESSA rather than the vendor's own description.
Keep reading
- ESSA evidence tiers explained: what Tier 1, 2, and 3 mean for your curriculum purchase
- What is structured literacy?
- What is the science of reading? A guide for school leaders
- What science of reading professional development should include
- Sustained literacy coaching for schools
ESSA's evidence tiers, including the Tier III "Promising" definition and the requirement that Section 1003 school-improvement interventions meet Tiers I–III, are defined in the Every Student Succeeds Act (ESEA as amended, § 8101(21)) and U.S. Department of Education guidance. Study-quality determinations reference the What Works Clearinghouse standards.
