No - not at all. It's clear from your question that you haven't grasped the different grammatical structures involved in these two phrases. "John left for school" ---> Sentence in the ACTIVE voice. 'School' is a NOUN, referring to John's DESTINATION When you say 'John left for school', it is John himself who did the leaving. It probably means that John left his house in the morning in order to go to school. This is the same as saying 'I left for the airport' or 'I left for work'. It means that you leave one place, and go in the direction of another place. "John was left for dead" ---> Sentence in the PASSIVE voice. 'Dead' is an ADJECTIVE, referring to John's supposed STATE. When you say 'John was left for dead', it was another person who did the leaving. It means that someone left John, presuming that that he was dead. Maybe a violent mugger stole John's wallet, beat him up, and left him lying in a pool of blood. The mugger thought that John was dead, and he left him in this state. I hope that is clear. Remember, to understand English properly it isn't enough to look at individual words - you need to understand the underlying grammar which connects those words.

No. "Left for dead," means that somebody who is very seriously injured was left in that state - no attempt was made to help him or her. Example sentence: "The criminals beat up the 85 year old lady, seriously injuring her, before leaving her for dead as they ran off with her purse."