**Table 1. Analytic samples and participation patterns**

| Grade band | System | Students | Schools | JRR zones | Both-wave *n* | Baseline-only *n* | Follow-up-only *n* | Both-wave weighted % |
| --- | --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: |
| Grades 4–5 | Georgia | 4,491 | 156 | 79 | 3,787 | 624 | 80 | 84.3 |
| Grades 4–5 | Italy | 4,610 | 152 | 76 | 4,207 | 246 | 157 | 91.6 |
| Grades 4–5 | Jordan | 6,172 | 224 | 115 | 5,141 | 924 | 107 | 81.9 |
| Grades 4–5 | Republic of Korea | 4,507 | 156 | 78 | 3,558 | 797 | 152 | 81.3 |
| Grades 4–5 | Kosovo | 4,747 | 152 | 86 | 4,190 | 419 | 138 | 88.3 |
| Grades 4–5 | Montenegro | 4,559 | 141 | 125 | 4,150 | 267 | 142 | 90.8 |
| Grades 4–5 | North Macedonia | 4,866 | 150 | 87 | 4,137 | 505 | 224 | 85.2 |
| Grades 4–5 | Slovenia | 5,015 | 149 | 75 | 4,104 | 642 | 269 | 82.4 |
| Grades 4–5 | Sweden | 5,358 | 160 | 81 | 4,436 | 703 | 219 | 82.9 |
| Grades 8–9 | Jordan | 7,051 | 225 | 114 | 5,921 | 1,041 | 89 | 81.6 |
| Grades 8–9 | Republic of Korea | 4,410 | 176 | 88 | 3,845 | 412 | 153 | 86.7 |
| Grades 8–9 | Sweden | 5,303 | 154 | 78 | 4,358 | 724 | 221 | 82.5 |

*Note.* JRR = jackknife repeated replication. A wave is marked participated when either relevant process flag equals 1; source codes were gated to {1, 2}. No students were classified as participating in neither wave in the linked analytic files. Weighted percentages use the final student weight (TOTWGT).
