The pint-sized pupils in Paula Merrigan’s transitional kindergarten, or TK, class often call her mom, or sometimes even grandma. One reason there’s such a strong teacher-student bond boils down to warmth. Merrigan makes sure all the children are greeted with a big smile when they enter the classroom in the morning, she works with every single one of them one-on-one at some point during the day, and she is generous with praise, hugs and affection.