Sumo is a... kid who grew up on the right side of the wrong side of the tracks.
I don’t think it would be wrong of me to assume that it’s not uncommon for members of Sumo’s family and the people he associated with before meeting Clarence to see school as something that isn’t mandatory. It’s all more noticeable because Sumo has many siblings that look around his age, and I know the episodes are mostly confined to Clarence/Sumo/Jeff’s class, but maybe I’m too used to Bob’s Burgers where somehow the siblings manage to run into each other at school.
Sumo really reminds me of Shawn Hunter from Boy Meets World - overall he’s a good and kind kid with maybe not the most privileged of upbringing. More importantly, I’m glad Clarence and Jeff, like Cory from BMW, don’t think of him as any less as a result of his financial/social situation.