Students with diagnosed learning disabilities have IEPs assigned to them, and it is literally illegal for teachers to not implement what is on the IEP for the student. This means most of the time they get modified tests, modified assignments, and a modified grading scale, which is adjusted for every single student individually. The accommodations are in place and, as long as the teacher is implementing them as they are legally obligated to, the student should still be able to pass.
With that being said, yes, it is certainly much harder for them to pass. And if a teacher is not implementing the accommodations, then it is on them and they can be fired. As a teacher and a coach, I get the frustration from both sides. Last season a basketball player with an F in my class played a game and I threw a fit to the athletic director because academics are the focus of school, so the kid was removed entirely from the team and the coach placed on probation for breaking school policy on ineligibility. As a coach, I hate getting that list and seeing kids are ineligible - it destroys me taking them out of the routine, but I understand why the rule is in place.
I had a policy this year that I would take girls out of every routine if they had a D, even though only F's are required to sit per school policy. This way, if that D did drop to an F and they were officially out, I didn't have to rearrange my entire routine because they already weren't in it. Trust me, those girls kicked their cute little booties into gear the first time I made one of them sit for a D, and I haven't had any issues since. But you gotta stick to it, or they'll let their grades drop and you might lose one at the last second.
Talking to the teachers helps - if a student has a bad grade because I haven't entered assignments that were turned in over a week ago, I'll always say "hey, this is my fault, let me enter that assignment and if it brings their grade up I'll email the AD directly to let them know it was my mistake and the kid should be cleared." However, teachers need at least a week to grade things, so if you have a kid saying "Well I turned in my essay late but I got it in the day before grade checks!", then that isn't on the teacher, it's on the athlete for turning it in late and expecting it to show up right away on their grade.
I rambled a lot. Ineligibility is a topic I get really heated on, both as a teacher and as a coach, but what it boils down to is "Hey, school is why you're here, and if you need to sit and study during games/competitions instead of performing then you will do that." The only exception I had to my D rule was if it dropped to a D the week of a competition - I'm not going to rearrange the routine the week of unless they're told they have to sit by the AD.