Answer:
I would say that the best revision to sentence 6 is the first fragment: "Although many still claim that evidence about year-round school and its link to higher achievement is inconclusive, studies consistently reveal that year-round students score higher on certain assessments than those students who attend schools with traditional nine-month calendars."
It is the fragment with the most appropriate and respectful tone since it mentions the consistency of certain studies and supports the main clain with those studies and their revelations, using an ethos rethorical approach.
The other options do not provide other sources of information to support the main claim, and they focus on discrediting the counterclaimants or even regarding them in a paternalistic way.
Explanation:
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