To collect information about the ability composition of the student intake into the primary grades, TIMSS asked school principals to estimate the percentage of students in the school who possess a range of literacy and numeracy skills when beginning primary school (see About the Scale in Exhibit 6.10).

Exhibits 6.11 and 6.12 present the percentages of students in each of three groups of schools categorized by their principals’ reports, together with average mathematics and science achievement, respectively. There was considerable variation across countries in the percentage of students in the highest category—“more than 75% enter with skills”—from 89 percent in Ireland, where many students start preprimary school after their fourth birthday (as described in the TIMSS 2019 Encyclopedia), to 0 percent in the Czech Republic and Hungary. On average, 24 percent of students were in schools where “more than 75%” of the students entered school with literacy and numeracy skills, 56 percent were in schools where “25–75%” entered with such skills, and 20 percent in schools where “less than 25%” enter with literacy and numeracy skills.

For both mathematics and science, average achievement was higher for students in schools with greater percentages of entering students having literacy and numeracy skills. Students attending schools where “more than 75% enter with skills” had the highest achievement, followed by schools where “25–75% enter with skills,” and students in schools with “less than 25%” having the lowest average achievement (508, 499, and 480, respectively, for mathematics and 499, 490, and 471, respectively, for science).