The most basic decision is selecting and defining the specific structure and components of the service delivery system that will be used. Current RTI implementation models use a generally similar structure with some common components, but they also show variations. Some initiatives include relatively rigid tiers, while in others the number of tiers varies in different school districts, depending on resources and other factors. For example, a district might adopt a “standard protocol” model with two fairly rigid tiers (e.g., a single type of remedial program as the sole basis for assessing RTI) or a multitiered model having three more flexible tiers. The model and components selected will influence the personnel, resources, and decision-making processes to be implemented.