IEP eligibility for spelling only depends on the state regs and district practices, and on the impact on the student's access to an education. Technically, spelling is part of a specific learning disability in written expression. At the high school level, typically it just gets accommodated (most of those students have had years of remediation in phonics and spelling, and have likely maxed out on benefit; it's just diminishing returns to continue at this point). At the elementary level, it's typically worth remediating, as it can have real impacts on written expression. During the middle school years, I think it's pretty individual, and depends quite a bit on the presence or absence of a history of OG/phonics remediation with fidelity.
But I would agree that the classification matters much less than the access to remediation. SRA approaches do have their own positive history. It's a bit of a different approach than OG. And sometimes, it's just that there has been limited systematic instruction of any kind in spelling, as many schools have deemphasized spelling even in the younger grades.
BTW, geofizz, I had a student once who essentially had two forms of the same language as well. Also severely reading disabled, but with very effective reading comprehension. The origin of the deficit was probably a bit different from your kiddos', but the net result was the same: no sound-symbol correspondence.
