It’s actually kinda nice because the student’s level of obesity might be enough to make them bed bound, so they’d still getting an education while not being able to be there. Fat shaming is still a thing, even at elementary levels. If the student is too big to move around too long, then walking in the hallways will most likely make them faint. There’s no context as to how obese the child is, so it’s kinda rude to say it’s disgusting [more or less insulting]. 

There may be other factors why this boy doesn’t attend school physically other than his obesity. Such as allergens or other medical problems.

Oh look I googled his name and found WHY he doesn’t attend school!

“The boy’s extreme allergies prevent him from doing many of the things that kids his age do. ”

*edit* “Devon’s allergies are so severe that, according to The Sun, interacting with other children could kill him. His diet consists primarily of corn, apples, and potatoes.” [/edit]

Source: http://www.huffingtonpost.com/2012/10/05/devon-carrow-robot-school_n_1942802.html

Please don’t go around insulting people without context. Insulting people is rude regardless, so just don’t do it unless it’s Justin Bieber.