posted by rfvv .
1. I'm in the third year of middle school.
2. I'm in the third year in middle school.
(Which preposition do we have to use?)
3. My school is a boys-only school.
4. My school is a boys' school.
5. My school is girls-only school.
6. My school is a girls' school.
(Are all OK? Which ones are commonly used?)
1 and 2 - Both prepositions are fine in this construction.
3 - 6 - All are OK. 4 and 6 are most commonly used.