MITCHELL — A handful of students sat at desks at Longfellow Elementary School earlier this week, heads bowed in concentration on the worksheets in front of them. Moving among them, a few adults checked in on students as they worked on identifying the numbers. Abby Vermeulen paused at a desk and sat down across from a puzzled student. She gently offered up some advice and a few questions, and soon the student was making his way down his worksheet…