I need some help to correct my grammatical errors in English.
In my English textbook, I found several places I don't understand. The first one goes like "I'm in tenth grade in Senior High school." My question is whether "the" is necessary before the word tenth and whether senior high has to be capitalized. The second one is "At the end of twelfth grade, American students receive the high school diploma." I want to know whether I have to change diploma to its plural form.