Please read the following sentence
- He is in Mclean High school.
- He was in McLean High School.
If we convert them into questions then
- Is he in Mclean High School?
- Was he in McLean High School?
Same question adding the question word 'which'
- Which school is he in?
- Which school was he in?
But I suppose that's not the way native Americans ask these questions but they ask like
- Which school does he go to?
- Which school did he go to?
What is the difference in 'which' questions and is it ok to ask someone 'Which school were you in?'