Answer to Question 1
Given the information presented in the case, there is no way to know for sure. There are at least three possible reasons:
Perhaps Seth's family does not value academic achievement, in which case good grades are not an incentive for Seth.
Seth may have poor mathematical skills that he is trying to hide by pretending he doesn't care about the assigned problems.
Individual accountability for learning is often critical for the success of cooperative learning activities: All group members should individually demonstrate that they have mastered the material. In this case, we see no individual accountability. A single sheet of paper is turned in that gives all group members equal credit for problem solutions.
Answer to Question 2
Teasing in a way that fosters teacher-student relationships is acceptable, but teasing in a way that undermines self-esteem is clearly inappropriate. In this situation, Ms. Wyatt seems to be using teasing to foster a friendly relationship with the boys. She should do so only if she's confident that the boys will not find her comments embarrassing.