You know I pulled these figures out of their table on the bus in to work. I selected the largest economies in the OECD (Germany, France, America, South Korean and Japan are the largest economies in the OECD). I added Taiwan and Singapore for context since my contention related to east Asia and only two countries is unbalanced. I should have added UK (-9) instead of Sweden (all the Brexit dooming made me forget that the UK is still a bigger economy and I actually buy some Swedish stuff). As for your list - it seems very arbitrary. Sweden is a good proxy for Finland and they share the same exact trend. Israel is the only other OECD country on your list. The rest are simply random non-OECD countries.

Since you and others have brought up immigration I felt the need to review this thesis. For the OECD plotting foreign born population against Pisa math changes gets a decent correlation (Spearman r = −0.384; p = 0.017). Obviously foreign born is an imperfect proxy for classroom demographics, but it's a start. Definitely a trend, not a huge one, but hard to ignore. I'm honestly surprised that it is not discussed much in a 400 page report with correlation plots between composite indices (a sign of a very extensive data analytics project). Total failure on the part of the researchers). Putting aside any racial claims, I would leave open the possibility that training a large percentage of kids in a language they don't really understand is not likely be be as effective as speaking a language that they do understand. Seems pretty obvious actually. In fact if you drop the English speaking countries from the OECD list (English is very commonly spoken across the globe), then the correlation coefficient goes up to −0.55; p = 0.001).