Re: Anything wrong with my note for UPS deliveryman?
Traditionally, "junior high" is 7th and 8th grade - ages 12-14 or so.
"Middle school" usually starts in 6th grade, so it's 6th, 7th, and 8th.
I understand that the "junior high" that I went to as a child is now a middle school.
I don't hear the term "senior high school" used that much -- usually it's just "high school," but the terms are synonymous - grades 9-12, or ages 14-18 (more or less).
Adding to the fun, we use "school" in the US to mean college/university, so if you say "My kids are still in school" it could mean they are 5 or 22." And if you say "Where did you go to school?" it means "where did you go to college/university."
And finally, we don't really differentiate between college/university. I've seen other sites where someone has given entirely wrong information, saying a college is less prestigious and doesn't offere the same degree. Both a college and a university award bachelor's degrees.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.