RTII stands for Response to Instruction and Intervention. Schools use RTII to provide extra help to the struggling students by tracking, supporting, monitoring and providing intervention to all students in a whole class or group setting based upon individual needs. The overall goal of RTII is to ensure that intervention occurs as soon as possible so that nobody falls short of their expected goals.
The following link will provide you with instructional strategies and instructional activities that can be used for each tier of RTII.
https://www.letslearnandgrow.com/instructional-strategies-for-rtii5.html