“Lauren knew she wanted to be a newscaster in the 4th grade.”
She had other ideas for 5th grade, I guess.
Actually, I think Lauren knew in the 4th grade that she wanted to be a newscaster.
English wants each word or phrase to modify the most recent prior word or phrase — at least as much as is feasible.
So it’s dangerous to delay a phrase like “in the 4th grade” all the way to the end of the sentence.
Put “in the 4th grade” immediately after the word it refers to — in this case, “knew.”
All bets are off, however, if Lauren actually had an idea to broadcast a news show from Mrs. Helfin’s room at Franklin Elementary. Which might be awesome.