A review of the English school curriculum is currently underway. The review's recently released interim report makes clear that the current education system is not working well for all young people - in particular those with special educational needs and from more deprived backgrounds.

However, the report does not recommend radical change. It proposes sticking with the curriculum approach brought in through reforms over the last decade or so under the previous Conservative government, but that these need to be built on to have a more inclusive approach.

In 2014, there were significant changes in the national curriculum and to GCSE exams. These changes were branded a "knowledge-rich" curriculum, which meant more content to learn and a greater emphasis on memorising and final exams.

Defenders of the changes, such as former schools minister Nick Gibb, say that the success of this curriculum is shown by improvements in England's performance in the Programme for International Student Assessment (Pisa). This is a global series of tests for 15-year-olds in maths, science and reading, taken in each country's national language, that run usually every three years.

In 2022, the most recent round of tests, England's country rank was 14th for maths, 14th for science and 13th for reading out of 81 countries. This compares with 2009's rankings of 28th for maths, 16th for science and 25th for reading.

The story is that Pisa tests dropped in the noughties due to a "skills-based curriculum" but have risen under a knowledge-rich curriculum. Pisa is important to this argument because the changes to national examinations in England mean GCSE exam results 20 years ago cannot be directly compared with GCSE results today. The curriculum review interim report notes that England's results compare well internationally.

However, this proof of the success of a knowledge-rich curriculum is not clear cut. To understand why, we need to look at the Pisa tests and how Pisa sampling works, the importance of not cherry-picking evidence, and what has really changed and not changed in the curriculum in England.

To compare two people's knowledge or how the knowledge of the same person changes over time, the same or equivalent tests need to be used. But the Pisa tests taken in 2022 are not the same as the ones taken previously. Each time Pisa tests are taken, some items from the last test are kept but other items are added. There are various ways that the OECD, who run Pisa, try to make sure that tests are equivalent, but changes do make a difference.

What's more, Pisa is not usually a test of everyone in a country. The government's official research report on the 2022 Pisa results states that higher performing pupils were overrepresented and disadvantaged pupils underrepresented.

Adjusting for the bias in the sample, the OECD estimated that the 2022 result might have been up to eight points lower. Still above the OECD national averages but very similar to 2009, and so hardly the resounding success claimed by some.

More generally, we need to be careful that evidence isn't being cherry-picked - choosing the evidence that supports a case rather than all the evidence. Any success in Pisa 2022 for England appears to be due to success for those already doing well. The gap between advantaged and disadvantaged pupils in England is not closing. This backs up the headline goal of the curriculum review - to improve the curriculum so it works better for everyone.

Regardless of pupil performance, the pupil survey done alongside the test contained some worrying findings. Pupils reported the second lowest levels of life satisfaction across OECD countries, and headteachers said that difficulties recruiting teachers are negatively affecting pupils.

Pisa scores were not the main reason for changing the curriculum in 2014 in England. They were used to justify the changes. But the amount of change is overstated, and this also undermines the claims made for the success of the current curriculum and also the fear that any change would undermine England's comparative success in tests like Pisa.

It is a myth that the before the 2014 curriculum reforms, England had a skills-based national curriculum. With colleagues, I looked at skills in the curriculum in England in the past and now and found that generic life skills were hardly mentioned before the reforms. Looking at maths, the content of the curriculum hasn't changed much at all.

We also compared the current curriculum in England with other countries that do better than England in Pisa and are also seen as examples of knowledge-rich systems. These include Singapore, the world leader, and Estonia, who are top in Europe. What we found is that those countries' Pisa success is based on a curriculum that works better for everyone.

Part of that comes from including aspects of a skills-based approach. These curricula balance a focus on knowledge with inclusion of skills, particularly digital literacy. They pay attention to making sure school is a good basis for vocational education, working life and taking part in society, and not only for further academic study.

Taking a closer look at Pisa outcomes and the differences between our curriculum and other countries' backs up the central message of the curriculum review's interim report. The English system works well for some but not well for everyone, and could do better as an education system. It also points to practical lessons from countries like Singapore and Estonia about how vocational education and skills can be valued without losing sight of the importance of knowledge.