DH was a teacher for a private agency (not a school district). When he started there, they paid teachers year round, 1/26 of salary. If you worked the optional Summer School, you got an additional checks for those weeks at 1/21 of salary. They decided to change teacher pay (but not other staff) to only be paid during the school year at 1/21 of salary, and nothing during the average 10 weeks of summer vacation, unless you worked Summer School (which only ran the middle 6 weeks).
So when this new scheme went into effect, employees were surprised to not receive a paycheck until late September (after 2 weeks work + 1 week lag). There was so much complaining, the employer eventually cut them an early paycheck, with the understanding that it was an advance, which would come off the end of the year. By June, everyone had forgotten the advance, and were once again surprised to have no more paycheck, even earlier than planned.
Once year round checks were discontinued, another anomaly occurred: occasionally the school year would not sync with the 21 biweekly paycheck schedule. They would have another week or two to work beyond the last payroll period! School year can be 43 weeks instead of the normal 42, but you only get the 21 paychecks. However, if the summer vacation fluctuated to 11 weeks, your next year's pay schedule was off by a week (you lost that 1/2 paycheck, in a calendar year, effectively).