Thanks for your comments (and for your feedback on the experience of posting a response to this blog, which I will pass along). The ultimate aim is that the PISA for Development results would be placed on the same scale as the regular PISA so hopefully your wish will be granted! In addition, the PISA for Development ‘option’ is meant to be folded into the regular PISA program so that it all becomes one assessment exercise that includes different options for countries in terms of the types of test booklets, questionnaires, and sampling approaches they use to gauge the achievement levels of their 15-year-olds. All countries' results will be placed on the same scale. You’re right that comparisons among countries is one reason why PISA is so useful and that’s something that the PISA for Development initiative wants to preserve (in part by drawing on existing items from the secure PISA item pool that have been used in earlier PISA exercises – this helps create the link that you refer to in your comments). Whether it can achieve this is another issue.