自习 vs 自学: what's the difference? What's the difference among:


自习     (zì xí)   
自学     (zì xué)  


They should be something like "to study by oneself", "to study on one’s own", but still, I don't get the difference.
自习 is more frequently related to the "self-study sessions" of high-school and colleges.  

自学 generally implies teaching oneself about sth., i.e. no connotation to schools.