me_irl

We have them in Canada, I assume they work the same:

When your work is assessed, you get a letter grade in the range from A-F. E is absent, although some regions will use E instead of F. Your letter grade is determined by your percentage.

Letter grades aren't super useful to show your overall results, and are difficult to average, so they can be converted back into numbers. You start at 0 for F, then skip over E to get to D which is worth 1.0, C is 2.0, etc. GPA doesn't go higher than 4.0 at A, or 85%, so there's actually quite a lot of margin for error to allow people the maximum GPA if they test well.

Oh, and your letters might get a + or - to show you're on the high or low end of a grade. There's a lot of range between a C and a B, but C+ is close to B-. A + is worth 0.3 on your GPA, and a - is worth -0.3

Also, your letter grades and therefore numeric GPA is a non-linear scale, and the conversion for what percentage converts to which letter might differ depending on the institution, school district, or region.

Isn't it so simple?

Valedictorian is a bit easier to understand. At graduation, one student is selected to be Valedictorian, and their function is to give a speech at the graduation ceremony.

Traditionally, it's the "highest performing" student, but GPA caps out at 4.0 which means that two students with an 87% and 98% average have the same GPA and are therefore equal. Their social achievements are then considered, so the valedictorian will usually be someone who was very active in extracurricular clubs or sports.

Basically Valedictorian is usually the most popular student who got straight As.