I studied in ABC school from 2013 to 2020. I graduated from that school in the year 2020. I was admitted to the school in grade VI, and progressed up to grade XII. The system is similar to the K-12 system in America. I am currently studying in a college.
I want to emphasize on the fact that I was in class VI when I was admitted to ABC School (I studied there for a long time).
The following sentence does not sound correct to me:
I had been studying in ABC School since class VI.
In order to be able to use past perfect continuous, there should be a reference in the past. For example: X had been happening until Y happened.
I cannot use present perfect continuous because I'm no longer studying in that school.
As per me, this should be correct:
I was a student of ABC School since class VI.
What should be the correct sentence structure in this case?