Principals’ categorizations of their schools according to the percentage of fourth grade students who spoke the language of the TIMSS 2019 assessment as their first language are shown in Exhibit 6.6, together with average mathematics achievement, and in Exhibit 6.7 together with science achievement. On average, 63 percent were in schools where most students (more than 90%) spoke the language of the TIMSS assessment as their first language, and another 18 percent were in schools where more than half of students (51–90%) spoke the language of the assessment as their first language. Both groups of students had higher average achievement than the 19 percent of students attending schools where only half of the students (or less) spoke the language of the assessment as their native language (506 and 501 vs. 486 for mathematics, and 498 and 493 vs. 471 for science).

As shown in Exhibit 6.8 for mathematics and in Exhibit 6.9 for science, the distribution of eighth grade students across the language composition groups was similar to fourth grade. Sixty-four percent of students were in schools where most students spoke the assessment language as their first language (more than 90%) and 17 percent and 18 percent were in schools where more than half of the students (51–90%) and only half of the students (or less) did so, respectively. There was little difference in average mathematics or science achievement among the groups, although average science achievement was lower in schools where only half of the students (or less) spoke the language of the assessment as their native language (483 vs. 484 and 487 for mathematics, and 479 vs. 491 and 490 for science).