YOU SAID:

I was the biggest boy in the class from the 1st grade untill the senior year at highscholl

INTO JAPANESE

私は高校１年生から高校１年生までクラスで最大の少年でした

BACK INTO ENGLISH

I was the biggest boy in my class from first year high school to first year high school

INTO JAPANESE

私は高校1年生から高校1年生までのクラスで最大の少年でした

BACK INTO ENGLISH

I was the biggest boy in the class from high school first grade to high school first grade

INTO JAPANESE

私は高校1年生から高校1年生までのクラスで最大の少年でした

BACK INTO ENGLISH

I was the biggest boy in the class from high school first grade to high school first grade