This tweet went out from SPS:
School will start Thursday! We are excited to welcome our 53,000 students! Reminder: kindergartners will also start Thurs.
EXCEPT, as The Stranger accurately points out, there is no firm agreement yet with the union. The union hasn't tweeted this news. This is a tactic that is often used when tentative agreements are made in order to embarrass/force one party to agree to a contract.
While I think it is more than likely school will start Thursday, it was wrong of the district to say so not in unison with the union.