When Chelsea Silbereis’ son came home from school last week, he was nauseous, fatigued, and suffering from a headache. He was not alone. Parents and educators gathered at the School Committee meeting on June 16 to raise concerns over excessive heat in elementary schools across the school district. During last week’s heat wave and into early this week, classroom temperatures at Burbank Elementary School and Winn Brook Elementary School reached nearly 90 degrees. “It’s not just that you need to…