As shown in Exhibit 6.1, TIMSS characterizes schools in terms of socioeconomic composition based on principals’ reports of the percentages of economically disadvantaged and economically affluent students in the school (see About the Scale). “More affluent” schools were defined as having more than 25 percent of students from economically affluent homes and not more than 25 percent from economically disadvantaged homes, while “more disadvantaged” schools had more than 25 percent of students from disadvantaged homes and not more than 25 percent from affluent homes. All other combinations were considered to be “neither more affluent nor more disadvantaged.”

Exhibits 6.2 and 6.3 present the percentages of fourth grade students in each category in relation to mathematics achievement and science achievement, respectively. At fourth grade, 41 percent of students, on average, were in schools with relatively more affluent students than disadvantaged students, 34 percent were in schools where there was a balance, and 25 percent were in schools with relatively more disadvantaged than affluent students. Average achievement was highest for students in the “more affluent” schools for both mathematics (521) and science (512) and lowest in the “more disadvantaged” schools (479 and 467 for mathematics and science, respectively). Average achievement for students attending “neither more affluent nor more disadvantaged” schools was in the middle (499 for mathematics and 489 for science).

Exhibits 6.4 and 6.5 present the percentages of eighth grade students in each category in relation to mathematics achievement and science achievement, respectively. Compared with the fourth grade, the distribution of eighth grade students was more even across the school composition groups, with 35 percent in schools with relatively more affluent students than disadvantaged students, 33 percent in schools where there was a balance, and 32 percent in schools with relatively more disadvantaged students than affluent students. The relationship with achievement was similar to fourth grade, with average achievement highest for students in “more affluent” schools for both mathematics (518) and science (518) and lowest in the “more disadvantaged” schools (466 and 468 for mathematics and science, respectively). Average achievement for students attending “neither more affluent nor more disadvantaged” schools was in the middle (489 for mathematics and 490 for science).