RtI is a framework that crosses general and special education. Not only is it supposed to be "don't wait until the IEP process is finished", but also "don't withhold help because a child doesn't qualify for an IEP".
Tier 1 is a quality, evidence-based core curriculum implemented with fidelity for all students. For academics, this means using a research-supported reading, math, etc. curriculum, such as a reading curriculum with explicit instruction in the Big 5 reading skills, including phonological processing and phonics. For behavior, this could be a class/school-wide positive behavior support system. For EF, this might be agendabooks, organizers, or online assignment-tracking and communication systems (like edline or teacherweb), scaffolding/benchmarks for multi-part assignments that the teacher presents to the whole class.
Basically, anything that is presented to every student is tier 1. Teachers skilled in UDL (universal design for learning) tend to have a great many strategies usually thought of as tier 2 already programmed into their tier 1 instruction.
Tier 2 is usually standardized small group interventions. These may be pull-out, push-in, or implemented by the regular teacher. Academic examples would be grouping reading instruction by high, middle, low reading levels, or pull-out remedial reading instruction. An EF (or behavior) example might be having a list of children on check-in/check-out of some kind, such as initialing the agendabook, or collecting homework for all subjects first thing in the morning (before they have a chance to get lost).
Tier 3 is more intensive individualized interventions. A minority of schools actually offer OG or Wilson reading as an RtI tier 3 intervention. An individualized behavior support plan would be tier 3. I'd put developing and monitoring a personal organization flow for homework completion and return in tier 3.
Hypothetically, tier 3 supports should be available to any student who needs them regardless of sped status, but in practice, demonstrating need for tier 3 interventions tends to put children onto the IEP/504 track.
