4 level as children around the 5 th percentile in OECD countries. Thinking in terms of percentiles suggests that the median (or below) child in poor countries would be a candidate, or a near candidate, for disability-related support in the OECD-a sobering perspective.The focus on learning is more demanding, but also more meaningful, than a focus on mere access to schooling, because there is far more inequality in learning around the world, than there is in access to schooling. As an example, consider reading skills. A crude but serviceable index of worldwide inequality of this indicator, just within the PISA 2015 reading database, can be crafted by taking the percentage of students performing at or above an acceptable minimum level (Level 2 in PISA 2015 reading), taking the range of this percentage between the three highest and three lowest-performing countries, and dividing this by the median performance. That produces an index value of 0.81. Now, taking two indicators of access, namely the gross enrolment ratios for secondary and tertiary education (the next two access frontiers), a similar calculation yields 0.30 and 0.57 respectively, for the same countries. In a loose sense, and using a database that does not include the worst-off countries in the world, the inequality in learning outcomes is 170 percent greater than the inequality in access to secondary education, and 43 percent greater than the inequality in access to tertiary education. 6 Second, there is a great deal of focus on inequality in the SDGs. In the MDGs, since the goal was in any case 100 percent access, and access is a binary issue (one is either in school or not, one completes primary school or not 7 ), a goal of equality is implicit in a goal of 100 percent access. In addition, much of the declarative emphasis was on gender inequality. However, gender inequality is a relatively weak proxy for overall inequality. The SDGs are different. They emphasize inequality as created by quite a few factors (gender, region, income, disability, etc.). (Though they do not cover what one might call "pure" or "total" inequality, that is, the total dispersion in scores, due to factors such as income and region, but also, importantly, due to lack of quality assurance and standards.) This is an important lack in the SDGs, but researchers and policy-makers are likely to pay attention to the issue anyway. Moreover, learning outcomes are a much less binary and more complicated 6 Just to take a data point from within a developing region, in Latin America's TERCE Grade 6 reading results, the cognitive gap between the top two and bottom two performers, measured via the same index as in PISA 2015 reading (but in TERCE taking the top two performance levels, as the TERCE levels are much "easier" than PISA's), is 1.25, whereas the gaps in access to secondary and tertiary education respectively, are 0.31 and 0.53, respectively: the cognitive gap is 4 times larger than the gap in access to secondary education, and 2.3 times larger than the gap in access to tertiary e...