What it adds
Without a school account, every teacher runs their own classes in isolation. A school account gives you one roster, one set of reports, and school-level roles, so a head of department can see every class rather than only their own.
Who belongs to a school
A school has a School Owner (the person who created it, or the Account Manager for a government school), optional School Admins, Staff, Teachers and Students. Each person keeps their normal Meta Typing Club account and simply gains a membership in your school.
What it costs
Nothing. The school gets a 1-month free Pro trial with every limit removed, then moves to the Free plan automatically and keeps its account, classes and history for good.