quando estava no ensino médio

when I was in high school

→ quando
phrase Rare #34,833
when I was in high school The subject is understood from context, so it can also mean 'when he was in high school,' 'when she was in high school,' etc.
PO: Quando estava no ensino médio, eu jogava futebol todo dia.
EN: When I was in high school, I played soccer every day.

Eu li este livro quando estava no ensino médio.

I read this book when I was in high school.

Tom me disse que ele costumava tocar clarinete quando estava no ensino médio.

Tom told me that he used to play the clarinet when he was in high school.

Tive que estudar francês quando estava no ensino médio.

I had to study French when I was in high school.

Eu estudei francês quando estava no ensino médio.

I studied French when I was in high school.