While inequality gaps in child educational achievement narrowed between those in the lowest and middle groups in these countries, the study found that inequalities in health had widened.

In an overall ranking of the countries, Denmark is the leader, with relatively narrow inequality gaps between children at the low end of income distribution and those in the middle. The overall ranking is weakest for Turkey and Israel, which have the widest inequality gaps.

Disparities in child health, derived from a survey of school-age children that measured the frequency of their health complaints, widened in a majority of the countries, the study showed. The smallest gaps between children at the low end of income levels and those in the middle were found in Austria, Germany and Switzerland, and the largest were in Turkey and Israel.

The study also showed that Canada, France, Iceland and Sweden had fallen in the overall rankings when compared with their performances in recent years. France and Canada, which had been ranked in the middle of the rankings, now are in the bottom third. Iceland and Sweden, which had been toward the top, now are barely above the bottom third.

In the household income category, two of the wealthiest countries — Japan and the United States — were in the bottom third in terms of the relative income gap, which reflects how far the poorest children have fallen behind those in the middle tier. In the United States, the household income disparity between the poorest children and those in the middle is nearly 59 percent, and in Japan it is slightly higher.