Final answer:
To most improve sentence 7 of the student's editorial, it should specifically address why the current school calendars are outdated and inefficient, enhancing the strength of the argument for year-round schooling.
Step-by-step explanation:
To improve sentence 7 in the student's argumentative editorial, which currently states 'It is about time that we replaced our outdated and inefficient school calendars,' a more specific revision could clarify exactly why the current school calendars are considered outdated and inefficient. For instance, the sentence could be revised to say 'Given the evidence linking year-round schooling with higher academic performance, it is imperative that we reconsider and revamp our outdated, traditional nine-month school calendars that hinder our educational progress.' This not only reinforces the claim with a clear judgement but also succinctly encapsulates the author's argument about the inefficiency of current school schedules.