Well, where I grew up / went to school
Junior High was grade 7-9 High School in that province was grades 10-12 (ie, grade 9 didn't/doesn't have credits.)
Where I live now, there are multiple school districts in the same city and rules and names etc vary from district to district. however it seems that....
districts could have a middle school - which is grade 6-8, and then grade 9 students are in the high school
districts could have a junior high - which is grade 7-9, and high schools start with grade 10 - but grade 9 students do earn HS credits
in the district we live, with the nearby high school - if you are in the English based program you would do a Junior High and start in the high school in grade 10 - but if you are in French Immersion you would go to a middle school and start the high school in grade 9...