Just what we need - ignorance at the front of the classroom. There are clear differences to casual social conversation styles, classroom (academic) discourse, and the conventions needed in writing. This moron is handicapping his students if he does not have high expectations for his students to be writing with clarity and proper form. If one of the teachers I work with said anything like that I'd be on him in a hot minute - and for a looooooong time.
In a science class he has other content, vocabulary, and processes to teach and assess. So spelling and grammar could be a secondary concern. But why would you not expect your 7th grader (or whichever grader) to be communicating in a manner that is at their grade level. Would this not be the standard that all students in the class are expected to work toward? This type of attitude is why so many students find themselves in college unprepared for the level of work. The STANDARD of English is represented in the manner in which our president speaks and in which the media commmunicates (speaking and writing). THAT is the standard for successful people in our society. Any teacher who does not have those standards for his/her students is not preparing them for their future properly and should not be in the field. Our kids can't afford to get less than that. It sounds to me like this teacher needs some continuing education. (Actually he sounds like a teacher making excuses for his laziness.) I would not want him in my kid's class.