It's almost tradition for players to blame their terrible teammates on kids who just got off school, but almost no one actually believes that statement. However, that isn't to say that matchmaking quality varies drastically depending on the day of the week.
A Redditor by the name of ThaITGuy decided to put this theory to the test and created two separate accounts, one that he only played on the weekend and one that he only played on weekdays. In an attempt to normalize results, he exclusively played support and only ever queued up by himself.
The results are surprising, to say the least. On the weekday account, ThaITGuy reached a total SR of 3287 with a win-loss record of 64-30-5. Meanwhile, on his weekend account, he only managed to reach an SR of 2773 and posted a record of 31-46-1. That's a pretty substantial difference, given that it's the same player.
The test ultimately has too many variables to be taken as gospel - after all, such a difference could have been a fluke - but it's still a pretty serious indication of matchmaking quality on weekends versus the weekday. Guess queuing up on a Monday morning is a good idea after all.