WASHINGTON, D.C. — At Center City public charter school Congress Heights, a group of about 25 first graders sit crossed-legged in front of Linda Kim as she reads to them about Ancient Egypt. Upstairs, Tamika Fernandez helps her fourth and fifth graders solve decimal problems on the whiteboard, while across the hall, Wendy Oftedahl’s class of seventh graders listen to author Karen Harrington talk about the writing process.