The months of March and April were a time of great unrest for the Spanish Government, which feared that the PISA Report, the most important education tests in the world, would be affected by an incident that occurred in Catalonia, a student exemption rate almost five times higher than allowed.
The Ministry of Education and Vocational Training detected the statistical anomaly in March and it was not until April 20 that the OECD, coordinator of the tests, communicated its final decision: the national report was not altered by the exceptionally high exemption rate recorded in Catalonia, but this autonomous community would appear in the report with a methodological warning indicating that its results would not be comparable with other countries or previous editions. Likewise, it was removed from the international report.
The Catalan sample constitutes only a part of the Spanish one, “so its impact is reduced”
The OECD explains the details of what happened.
This newspaper has also contacted the ministry, which remains tight-lipped on this issue, postponing possible explanations until September 8 when the report is published in all countries worldwide. Nor has the Department of Education and Vocational Training provided more details than those offered at the press conference and in the Parliament, through the minister, at the end of July, arguing that the matter is under confidential proceedings.
“The OECD, through the International PISA Consortium, responsible for administering the report, calculates the exclusion rates and communicates them to the participating countries,” explains the organization. These rates come from the information transferred by schools during the assessments, which were conducted between March and May 2025, recording students as present, absent, or excluded. An external company collects the data and sends it to the Consortium. It also calculates the participation rates of educational centers and the final weight of the sample.
“Therefore, participating countries do not know the exact exclusion rate until they receive the cleaned data (in January 2026) and its weighting (in March of the same year),” the organization emphasizes, “although they have a general idea of the national rate and that of their communities,” it continues.
What we know
What is PISA?
PISA (Programme for International Student Assessment) is the most important international education study in the world. It evaluates 15-year-old students in reading, mathematics, and science from 91 countries and numerous regions. This edition was conducted between March and May 2025. It is coordinated by the OECD.
What was the problem?
The OECD limits the proportion of students exempted from taking the test due to disability or not knowing the language because they arrived less than a year before to 5%. The exempted Catalan students, mostly due to disability, were 23.2% of the sample, which invalidates its representativeness. There was also 7% of students absent on the test day.
Was it detected?
The company contracted to supervise the test’s operation and collect data warned of a possible exclusion deviation to the National Institute of Educational Statistics (INEE), dependent on the ministry, which passed it on to the Higher Evaluation Council, coordinator of the test in Catalonia. But the technicians, according to ministry sources, did not escalate it to their superiors.
When did the administration officials find out?
Between January and March 2026 when the international organizers send the ministry the cleaned data file. Then, a high exclusion rate and the Catalonia incident are observed.
What did PISA decide?
After consulting with its technical bodies, on April 20 PISA communicated that Catalonia would appear in the Spanish national report, although with the technical note that its data would not be comparable with previous editions or other autonomous communities or countries. Its data represent the schools that participated, but do not represent the Catalan system.
What is the exclusion rate assigned to Spain?
It is unknown because it is information under strict embargo. It will be known on September 8 when the international report is published.
What steps has the administration taken?
The Generalitat, after learning of the incident in March, opened an informative proceeding that is still ongoing. It is confidential.
Who was responsible for overseeing the exclusion rate?
The Higher Evaluation Council. At the time of the test in spring 2025, this council had no president. The last one had been dismissed in 2024 for pointing out that the PISA sample was skewed with an excess of immigration. It was not replaced because Education anticipated the end of the Council with the implementation of the Agency for Prospection and Evaluation, an entity with more resources and more professionalized that started in July 2025. The Council depended on the Directorate General of Curriculum and the Secretariat of Educational Improvements.
Why do the proceedings take so long?
The difficulty of reconstructing the facts and the responsibilities attributed at each moment, according to Education sources. Documents and emails between institutions have been lost, and some people who held positions are no longer there.
Once the ministry receives the files provided by PISA technicians last March, it realizes the incident and, after analysis, sees that the exclusion rates of all autonomous communities are below the maximum rate established by PISA coordinators, 5% exclusion, except one, Catalonia, which presents an unusual 23.2%.
The ministry admitted a week ago that, in fact, it was alerted by the company contracted for data collection during the tests, 2E Estudios y Evaluaciones, conducted between March and May 2025. But the alarm remained at a technical level and was not escalated to political leaders. The same happened in Catalonia.
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The first thing the ministry does when it notices the incident and before the scheduled meeting with the OECD is to share its concern about the statistical finding with PISA technicians. At this stage, the consulted source clarifies, “the object of evaluation for PISA is the Spanish educational system, not its regions.”
The Paris-based organization then requested a review of the data by two internal bodies responsible for validating PISA’s methodological quality before deciding how to publish the results: the International PISA Consortium, which performs the calculations, and the Adjudication Group, which reviews whether the data meet international standards. This acts as an independent methodological guarantee body.
Its mission is to decide whether a country’s data meet the necessary quality standards to be internationally comparable and if a serious problem arises, it studies issues such as whether the sample is representative, if the exclusion rate is acceptable, if the participation of centers or students has been sufficient, if incidents occurred during the application, and ultimately, whether a country’s results can be published without reservations, with a methodological warning, or not published.
“This matter was examined, technically checked, debated, and finally resolved, with a publication criterion agreed upon by both technical teams,” add OECD sources. It is inferred that there were only technical exchanges and no political ones between Spain and the test organization.
The OECD does not reveal to this newspaper the resulting exclusion rate for Spain, because the report is under embargo. However, it points out that the Catalan sample constitutes only a part of the Spanish one, “therefore, the impact of a 23% exclusion rate is considerably reduced in the national results.”
For the Spanish sample, 30 Catalan centers were analyzed. The Generalitat expanded this sample by 21 more. Not all centers, according to the ministry, have exclusion rates above 5%. It remains to be seen whether Spain will appear with a methodological note or if the set of autonomous communities has cushioned Catalonia’s rate, which represents 14% of the Spanish educational system.
In previous PISA editions, some countries recorded exclusion rates between approximately 6% and 12%, “but never above 20%.”
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