In "olden days" pre-referral may not have started until students were significantly behind their peers and at risk of failure, and that process was the responsibility of Special Education Professionals. Now the Tier 1 pre-referral covers all students and begins with the classroom teacher.
This process begins with a Universal Screening tool to provide baseline data early in the year about students' performance in the areas of Literacy, Math and Behavior. Tools commonly used in Maine are NWEA, DRA, and previous end-of-year math competency tests.
These data are collected so that teachers know where to begin teaching and which students are ahead or behind. Additionally, the universal screening tool is an effectiveness measure for the core curriculum.
If the core curriculum at any particular grade level is effective, then about 70-80% of the students should be exactly where you expect them to be. The curriculum is more than standards; a curriculum should define what educators to need implement to reach their students. And, it includes all of the locally agreed upon materials, practices, assessments, time for instruction and expectations that each student needs at a particular level.
If, based on Universal Screening data, much less than 70-80% of students are not at expected levels, then you should explore shifts in core curricular practices. Also, at Tier 1, there is an expectation and an assurance that all programs were delivered to students with "fidelity."
Fidelity of implementation means a decision to use a program like Everyday Math has to be implemented properly with consistency. Within Tier 1, ongoing progress monitoring includes a system of formative and summative assessments to determine if teaching is helping students learn what is expected.