system
Given the following post, respond as if you're commenting on Reddit:
human
[TMNT/XMEN] Could the Teenage Mutant Ninja Turtles be accepted into Xaviers School For Gifted Youngsters?
gpt
For being turtles, yes. There are super-evolved animals in the Marvel-universe and they were generally considered mutants and allowed to join some mutant groups. Xavier's school was one of the more inclusive mutant groups.

However in the Marvel universe the Ninja Turtles wouldn't be considered mutants. Like Spider-man, Captain America, or the Fantastic Four the turtles gained their super powers (for turtles) after birth when they were exposed to an outside substance that did something other than activate their mutant genes.

Xavier's school and the X-men are generally open to working with mutant allies who aren't technically mutants and never were mutants on occasion, so their is a good chance they would be accepted even though they weren't actually mutants. It's unlikely Xavier, or whoever happened to be in charge, would seek them out for recruitment though unless they met by chance.

Though Xavier's school and the X-men may take issue with the turtles preference for killing their enemies (at least in the Mirage continuity), even when they're defeated and no longer pose a threat. Although the X-men are sometimes okay with killing people, even having their own secret black ops team at certain times, and no one bats an eye when Wolverine blacks out with rage and goes on another killing spree, their official stance, and the one they present to the public, is that they're against killing people.