Okay, let me first say that the British school system sounds amazing for someone that went to American schools all her life. Not all schools do it the same way, but here’s how my experience was:
The School System
There are approximately 4 levels of schooling here in America: Preschool, elementary school, middle school, and high school (there may be a level or so in between, but this is generally the structure). Elementary school starts at approximately 5-6 years old, and preschool is typically for 3-5 year olds (these are definitely approximations, it depends on a person’s birthday when deciding which grade they’ll be placed in). Elementary school is typically grades K (Kindergarten) to 5th (approximately 10-11 years old). From there you move on to middle school, 6-8, until you’re about 14 (or about to turn 14). High school is grades 9-12, and each year has its own name:
Grade 9: Freshman (14-15)
Grade 10: Sophomore (15-16)
Grade 11: Junior (16-17)
Grade 12: Senior (17-18)
Scheduling and GPA
Where I’m from, students are able to choose their schedules from grade 9 on (but there are still required classes each year, such as English (4 years), Math (3 years), Science (2 years), History (1.5 years)). Sophomore year (Grade 10) you’re required to take Drivers Ed, Speech, and Spanish (foreign language credit). You need 23 credits to graduate, which are earned by taking the required classes I listed above. There are other required classes as well, but I won’t go into them as I’m sure they won’t matter, and schools across America likely do it differently than mine did. GPA means Grade Point Average, it shows your overall grade average on a 4.0 scale unless it is weighted by AP classes (which are on a 5.0 scale and for advanced students). The numbers in the scale represent a letter grade each, the classic A, B, C, D, and F. Here’s the list of what they are:
5.0: A [Only achievable when an A is earned in an AP course]
4.0: A
3.0: B
2.0: C
1.0: D
0.0: F
Here’s an example of how a GPA would be calculated:
Let’s say these are a person’s grades:
English: B (3.0)
Math: B (3.0)
History: A (4.0)
P.E. (Physical Education): A (4.0)
Science: C (2.0)
Elective 1: A (4.0)
Elective 2: A (4.0)
Elective 3: B (3.0)
To calculate this person’s GPA, you’d first want to add all of the grade “worths”, we’ll call them, together. So that’d be 3.0 + 3.0 + 4.0 + 4.0 + 2.0 + 4.0 + 4.0 + 3.0 = 27.0. You would then divide that by 8 (or the amount of grades being used), which would get you 3.375. You would round to the nearest tenth to get the GPA, which, in this case, would be 3.4. That means the student would have a B centered GPA because the number falls in the B range.
School Days
A typical school days is about 7 hours here in America. Where I’m from, this is the typical schedule (very rounded, just for a general feel. Also not very accurate because I suck at making schedules):
Hour 1 (start of the day): 8-8:45
Hour 2: 8:50-9:45
Hour 3: 9:50-10:45
Hour 4: 10:50-11:45
Hour 5 (lunch): 11:50-12:20
Hour 6: 12:25-1:30
Hour 7: 1:35-2:50 [Home time]
Every school is different, this is just how my school was. The hours were all pretty much the same amount of time, I just suck at estimating.
School dances and other events you’d see in stories
Many of the listed events from your post revolve around American football. Homecoming, pep rallies, and spirit week all take place Homecoming week. Homecoming is always a home football game weekend, the game typically occurs on a Friday night with the dance occuring soon after. In the week leading up to the Homecoming game there is a spirit week; at my school, students of all grades would compete against the other grades for fun, Seniors (the oldest students) almost always won. Some competitions included dressing up to a spirit week dress up theme each day (like wacky Wednesday, country western/country club, school spirit aka school colors, pajama day, etc.), float building (I’ll explain this in depth in a moment), and finally performance at the pep rallies at the end of the week (Friday, the day of the game). The pep rallies were full of games played between the different grade levels, and even the teachers. After the school day, there was a Homecoming parade featuring floats created by each grade level (9-12), the Homecoming King and Queen (nominated the week of the Homecoming game and announced during the pep rally, not during the dance like many believe), and many other things that I can’t think of. Senior ditch day (or skip day) typically occurs the Monday after the Homecoming dance (which occurs near the end of September to early October), or after Prom (April or May). I never participated in these days to know enough about them, but only a handful of seniors from my school ever did them (usually those in general education classes, not in AP classes). As for the Fall Carnival and Sadie Hawkins Dance you mentioned, I don’t know what those are either, my school never had those.
I hope this helped to answer the questions you had about American high school! If you have any other questions, or if I missed anything, feel free to ask and I’ll do my best to answer them!