Where does “учесться” come from?
учесться (Russian) comes from Russian уче́сть, from Russian че́сть, from Old Church Slavonic чьсти, from Proto-Slavic čisti, from Proto-Balto-Slavic (s)keistéi, from Proto-Indo-European *(s)kʷéyt-t ~ *(s)kit-ént, from Proto-Indo-European kʷeyt- — to notice; to read.
учесться (Russian): passive of уче́сть
Ancestry of “учесться”, step by step