nhk world's moshe komata has the story. >> reporter: every three years the oecd sends out the program for the international student assessment. it tests 15 year olds from dozens of countries on science, math, reading and problem solving. 2015's grades are out. compared to their international peers, japanese students continue to rank high in math and science. but one score in particular is seen as cause for concern. japanese students dropped from fourth to eighth place on the reading test. experts and teachers are worried it's part of a trend that could get worse. they think today's digital world is hurting student vocabulary and also their comprehensive abilities. take this school in tokyo, for example. two years ago, they introduced tablets in the classroom. teachers say student motivation improved and so did grades. but they say there's a tradeoff. for one exercise, half of the class didn't even give an answer when they were asked to write their opinion based on the information that was given. and here is one of the reasons. >> translator: the tablet and the internet give answswers