You can create a “school work” mode and allocate separate access times for that mode such as 9:00am till 3:30pm on school days. Then when they are home they can switch back to fun mode manually which gives access time after school hours or before school hours.
You can have a time multiplier for a mode so for school work you could have a multiplier of zero* so that their time is not consumed, the school mode can be set up to only be available during school hours. (* At the time of writing, .01 is the lowest allowed multiplier, but this should be updated soon.)
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