And the winner is..
For the strangest misspelling seen multiple times this year...
Mixing up "whether" and "weather" is pretty common. Spell checking software is likely to miss it. And heck, if you didn't know that they were different words, one sounds as good as the other.
But "wheather" is sort of a hybrid. Perhaps these three students knew that it wasn't "weather", but couldn't couldn't bring themselves to write "whether" (always the misspelled word). I kind of like it. It is has a sort of woody feel to it, conjuring images of the heath.