To everyone confused on the student council's terms, let me explain. Student council serves for one year from around the beginning 2nd semester of year x to 1st semester of year x+1 (Japanese schools have 3 semesters a year).
Meaning:
Previous president's term: 2nd semester of his 1st year to 1st semester of his 2nd year
Shirogane's terms: 2nd semester of his 1st year to 1st semester of his 2nd year, and 2nd semester of his 2nd year to 1st semester of his 3rd year (meaning his second term will end a bit before he enters Stanford in September of his 3rd year)