It's great to read you are getting involved.
Did you speak to his counselor? You want to see all his standardized test scores since grade 1.
Do you have any teacher friends in the district who know the expertise of fellow employees? They can provide insight.
Do you have a reading specialist in the district?
Does your child have an EIP? Educational Improvement Plan
In New Jersey you can put in a request to meet with the Child Study Team.
Try this test out to corroborate your school report.
https://www.englishclub.com/reading/test.htm
Something doesn't seem right to me, good grades and poor test scores.
I wouldn't feel so confident this is something that you can fix with a handful of books in a DIY approach. He is already a sophomore. You need an educational improvement plan prepared by professionals that includes prepping for the PSAT if college is an option.
Uncle Tom's Cabin is probably not the best choice.
Reading Level :
high interest, readability grades 4 to 5
Vocabulary
Challenging words:
writing, ex-slave, cruelty, slavery, based, runaway, totally, entire, preacher, lasted, important, narrative, false, cruel, praise, impact
This might be a better fit. It’s a fun read too.
Joseph Heller Catch 22 or One Flew Over the Cuckoo’s Nest by Ken Kesey
Reading Level grades 9 to 12
Flesch-Kincaid grade level:
10.24
There are good lessons about dealing with authority figures.
Of course the biggest problem is the lack of trust problem. How do you know he is taking the test seriously? Some kids get bored, don't care or are tired and just bubble in anything to finish the test.
Why are you just finding out there is a reading [learning] problem?