assessment is diagnostic. Thus, it measures multiple skills used in the reading process. The weighted score was designed as a simple single score to use to measure growth for accountability reasons. Thus, comparing one score to another over a period of time will allow for a quick and easy method for measuring or reporting growth when funding sources require a single number for this purpose.
But using the weighted score to see if a student is at "grade level" is a statistically inaccurate method. For example, if a student was very low in one score and very high in another, the weighted score could make it seem like the student was at grade level. This is alway the case when multiple scores are arithmetically calculated into one number.
A better way might be to use the DORA profile letter. Students are given a profile letter from A to H. A to F represent particular profiles with specific gaps. All students with an H profile are at or above grade level; only H students are high in all areas.
A school district might also decide that for certain grade levels, other profile letters should be considered "on grade." For instance, in secondary, academic vocabulary is often very low and seems to plateau. So perhaps G-profiled students might also be considered "on grade" for 9th to 12th graders.