Freshmen here aiming for top level colleges. My school uses the following grading scale and doesn’t report the percentages.
AP/Dual Enrollment:
90-100 = A/5.0
80-89 = B/4.0
70-79 = C/3.0
etc.
Regular Classes:
90-100 = A/4.0
80-89 = B/3.0
70-79 = C/2.0
Will top colleges value my GPA significantly less because they don’t know if an A is a 90% or 100%?
No, this is pretty standard
No. But they will look at your school profile, which will give context about your GPA relative to your classmates, if your school does not rank.
Amplifying @skieurope’s post: your school will send a school profile which gives enough info that colleges will have a good idea where you fall in your class and the relative rigor of your courseload. AOs are used to a very wide range of school marking systems.
But: you do need to read this (even if MIT isn’t on your list, it holds true across the superselectives):
Colleges look at your school’s grading system in their school profile and judge relative to that (which is one of many reasons you are largely competing against your peers and the historical peers from your school more than the general pop).
Many colleges will compute their own GPA’s for you. Some ignore Freshman year, most ignore gym and other non-academic electives, some ignore or limit weighting for AP/IB/Honors classes, etc. Some won’t even look at your GPA but just look at your individual performances in academic classes. Most don’t share their methodologies. They best example that does is the UC system. They drop your Freshman and partial Senior year, drop all +/- grades and cap your ability to get extra points for AP/IB/Honors to the equivalent of 4 full year classes over your Sophomore and Junior year. So in that example, everyone at schools with +/- grades will end up computing no differently than you anyway. You could take 8 weighted classes a year at your school but the UC system would only count 4 total.
For top schools, this is where LORs and school/external awards come in and differentiate between the very talented and the person that just gets good grades. The LORs from the top student in a a HS will likely be much different than someone that “squeaks by” with all 90.50% even though they have a 4.0.
Correction on UC GPA calculation. 10-11th grades only from the a-g course requirements. (Summer prior to 10th to the Summer prior to 12th, no partial Senior year grades included.)
They also consider Unweighted UC GPA, Capped weighted UC GPA (8 semester of weighted classes) and Fully weighted UC GPA (unlimited semesters of weighted classes).