504s do not require triennial evaluations, like IEPs do, presumably because the disability is not transient, so once you've been documented as having a disability, you shouldn't need re-documentation of it, unless a new disability arises, or a new impact on basic life functions is reported. Since there are no modifications to content or need for specialized instruction, regular monitoring of academic progress is presumed to be unnecessary, beyond that maintained for nondisabled peers.
Now, if there is no documentation whatsoever of a disability (and RTI data would have to be fairly extensive to be documentation), then the legitimacy of the 504 existing at all comes into question. Needs and accommodations, on the other hand, can sometimes be (partially) identified through the data routinely collected by school and parents, such as, when I ask this student to clarify orally his responses on a written test, he comes up with a much higher quality response, which would bump him up a full letter grade. Therefore, supplementary oral assessment clearly allows him better access to demonstration of skills and concepts.
I agree that child find has an ongoing problem with inefficiency and subjectivity (not to mention budgetary considerations), but I would disagree that only parents are referring students for eligibility determination. In my experience, at least half of referrals come from school staff, either as direct referrals, or through at-risk channels. Also, there is a very wide range of eligibility standards in different school systems. IOW, child A will be a shoo-in for an IEP in district A, on a watch list, or receiving general ed supports in district B, and left to their own devices in district C. The category of district does not always line up the way you would expect it to, either, with the high-performing-ness of the district.
This forum is probably enriched for parents who have had to push the school district though, as, in practice, child find is biased toward below-grade level performance.
BTW, if the school district has reason to suspect that a child has a disability (such as if the parent presents evidence of a suspicion of a disability), even in the absence of documentation of eligibility, the district has an obligation to extend the due process protections for a disabled student to the child until such a time as they can document that the child does not have a disability.
