Complex sentence: Okie Paxton studied painting at the Cowles Art School, with Joseph DeCamp, Ernest Major, and another student William McGregor Paxton, during his brief tenure teaching at the school.
Split into simpler sentences: Okie Paxton studied painting at the Cowles Art School, with Joseph DeCamp and Ernest Major. She also took instruction from William McGregor Paxton, who had been a student at Cowles, during his brief tenure teaching at the school.