MIDDLEBORO — Prince the Labrador retriever, who works as an assistance dog at Henry B. Burkland Elementary School, has only been on the job for a few weeks, but he's already popular. On a late Friday morning, a class of first graders huddled around him the moment he reached the playground and asked if they could pet him. They remarked how soft he was, called him a good boy and asked his handler, adjustment counselor Erin Doak, if they could have him as their pet. "He just puts smiles on everyone's face," she said. "To me, he's definitely doing his job."