This topic's question is ambiguous on the type of school, so I will briefly discuss both high school and college.
Every subject in high school was taught poorly. If any piece of information stuck for a long period of time, outside of rote memorization, it really depended on the teacher's method of retaining information.
In regards to college, I'd say all general education subjects. Allow me to elaborate further.
For those that aren't aware - the first two years of any college undergraduate program in the US are typically filled with general education courses.
It does not matter if you went to a small lesser known junior college or even Harvard College, you will end up studying the same material as mandated by law and department of education.
I am aware of this knowledge as over the years, I have met and discussed these topics with people who studied and worked in various aspects of academic institutions across different levels (local, state, and federal).
The general education courses are basically remedial level courses, in which their main goal is to get all students across the board ready for their respective field of study. These courses are also prerequisites that students must take before taking higher level courses that pertain to their major.
I personally encountered this when I first attended community college as I did honors and advanced placement courses, only to learn that my college level courses were rehashing material I learned years prior...
What is worse is that I barely remember any of the material I learned in those years too...alongside others that I have met from different schools, even students from the Ivy Leagues!
Unfortunately, I have learned over the years since graduating that many colleges and universities have "levels" and "tiers" to these remedial courses as public school education has been falling across the US.
What shocked me was to see someone that I knew, take the same college math class four times before they finally passed it...and the class is only taught once a year!
(Additional note - you could test out of some general education courses, but there is only a small allowable limit of courses that would allow for that. There is also AP credit that students could transfer from high school, but only if the students could afford to take the class, book(s), and exam fee)