* A specific high school named Newman: Their percentiles would be based only on their students' ACT English scores, and would vary from year to year.
* A specific prep course or tutoring company: Their percentiles would reflect the scores of students who used their services. Again, this would vary by year and the makeup of their student body.
* A broader population (e.g., a demographic group): If referring to a particular demographic, the percentiles would be based on ACT data for that group.
To find the 25th-75th percentile range, you need to specify *which* Newman you're referring to and find their published data or contact them directly. The ACT itself publishes national percentile ranges, but those won't be specific to a "Newman" group.