This study examines emotional well-being variations among students (n = 13,398) across 5 countries during the COVID-19 pandemic. Secondary analysis is conducted using data from the "Responses to Educational Disruption Survey" (REDS), which focused on the pandemic experiences, including well-being, of 8th-grade students. The study constructs an emotional well-being scale employing bi-factor models and multidimensional item response theory, encompassing students' concerns, loneliness, social isolation, and negative emotions. Cross-analyses with gender and socioeconomic status (SES) reveal significant between-group disparities, measured by Cohen's d effect sizes. It uncovers gender gaps in emotional well-being, with girls consistently scoring lower in most countries. SES effects on emotional well-being vary among countries, with SES group distinctions generally smaller than gender disparities. Thus, gender appears to have played a more significant role than SES in relation to 8th-grade students' emotional well-being during the COVID-19 pandemic.