What do parents with their children during the summer, Christmas vacation, snow days, etc.? You said you don't want a babysitter you want an educator, but your concerns seem to be more about child care.
The time Iowa requires for children to be in school doesn't change with a four day week. The schools will either have longer days or more weeks so the kids will not be shorted time. The benefits for students are more qualified teachers as a 4 day week might entice those teachers to apply at the school even if the pay is lower. For example, this is what the Sidney elementary principal had to say about their staffing problems, "At the elementary, we had four positions that were unfilled this fall," said Wehling. "That resulted in some larger class sizes, getting creative using other staff members who are endorsed in other areas. That obviously creates more workload for other staff members, because they're wearing multiple hats. Of the four openings, we received zero applications."
As for your child care concerns, most schools considering the 4 day option are working on solutions for parents. Sidney is going to expand their before and after school programs to include a full day on the weekday regular school is not in session.