Social interdependence theory suggests that shared goals and individual accountability can support participation and writing development. However, evidence remains limited on how Teams Games Tournament (TGT) relates to individual explanatory writing and classroom engagement among primary learners of English as a foreign language. This study compared writing performance and observed engagement under TGT and conventional instruction in an Indonesian primary school. A quantitative quasi-experimental design involved 58 sixth-grade students in two intact classes: 28 received TGT, and 30 received conventional instruction across three lessons during regular classroom instruction. Data comprised individual writing pretests and posttests, observations using an eleven-indicator checklist, and a supplementary questionnaire administered only to the TGT class. Data were examined using descriptive statistics and a posttest comparison. Mean writing scores increased from 62.35 to 87.17 in TGT and from 63.93 to 66.13 in the comparison class, yielding a descriptive difference in mean changes of 22.62 points. Discussion, questioning, and classroom responses were more widely observed in TGT, whereas routine task completion showed smaller differences. Most TGT students reported positive experiences, although perceived writing benefits and emotional comfort were uneven. With one class per condition and no delayed assessment, these patterns cannot establish causal effectiveness or lasting gains. The findings suggest connecting team preparation and academic games with individual composing and feedback, while monitoring participation and emotional comfort separately. Such alignment may help teachers use cooperative activities to support the demands of explanatory writing without treating visible participation as sufficient evidence of individual learning.