My daughter will turn 12 this year, in 6th grade. So, in 8th grade, she will turn 14. In any case, which grades are in which school is more determined by space issues of the school district than anything else and people of my generation tend to use middle school and junior high interchangably, because we never heard of middle school til we had kids
I haven't ever figured out why they changed the name from Jr. High to middle school though. My daughter's experiences in middle school are very similar to mine in junior high (same structure, changing teachers each hour, type of electives, etc)