Final answer:
The question relates to Social Studies, focusing on the cultural significance of a soccer jersey that symbolizes transnational identities, appropriate for a high school level discussion.
Step-by-step explanation:
The subject of this question best fits under Social Studies due to the mention of a soccer jersey representing the transnational identities of Mexican-Americans. Such topics often delve into cultural studies, identity exploration, and the impact of social and political dynamics across borders, which are central themes in social science education. When discussing soccer in relation to national identity and the cultural significance of sports apparel, it is clear that the conversation transcends the mere physical aspect of soccer and delves into societal and cultural studies which are key components of Social Studies.
The grade level for this question seems to be High School as it touches upon complex social issues and the understanding of cultural symbols, which is typically explored at a higher educational level. Additionally, in a high school setting, students are expected to analyze and interpret the significance of symbols and cultural representations, as is the case with the implications of a soccer jersey featuring US and Mexico elements.