Table 4 Target population definitions of the respective studies

FIMS 1964

All pupils who are 13:0–13:11 years old at the date of testing and being in the grade containing the majority of pupils aged 13:0–13:11 years

FISS 1970

All students aged 14:0–14:11 years at the time of testing

SIMS 1980

All students in the grade in which the modal number of students has attained the age of 13:00 to 13:11 years by the middle of the school year

SISS 1984

All students aged 14:0–14:11 years old on the specified date of testing or all students in the grade where most 14-year-old students were to be found on the specified date of testing

TIMSS 1995

All students enrolled in the two adjacent grades that contain the largest proportion of students of age 13 years at the time of testing

TIMSS 1999

TIMSS in 1999 used the same definition as TIMSS 1995 to identify the target grades but assessed students in the upper of the two grades only, the eighth grade in most countries

TIMSS 2003

All students enrolled in the upper of the two adjacent grades that contain the largest proportion of 13-year-olds at the time of testing

TIMSS 2007

All students enrolled in the grade that represents eight years of formal schooling, counting from the first year of ISCED Level 1, provided that the mean age at the time of testing is at least 13.5 years

TIMSS 2011

Same as in 2007

TIMSS 2015

Same as in 2007

TIMSS 2019

Same as in 2007