How does Mrs. Starch learn what the kids are saying about her?

The correct choice reflects that Mrs. Starch is able to learn about what the kids are saying through a hearing aid, which implies that her ability to understand their conversations is assisted by this device. A hearing aid amplifies sound, allowing her to pick up on conversations that may otherwise be difficult to hear, especially in a potentially noisy environment like a classroom. This technology can significantly enhance her auditory perception, enabling her to become aware of the students' remarks without them being directly addressed to her.

In contrast, the other scenarios do not align with typical uses for dialogue between a teacher and students. For example, reading text messages would imply a breach of privacy and an expectation of undetected communication, which does not seem to reflect the dynamics of their relationship. Overhearing conversations is plausible but less direct than using a hearing aid, which specifically facilitates her hearing capability. The idea of using a spy camera introduces an element of deception and surveillance that contrasts with the teacher-student trust dynamic usually present in educational settings. This makes the answer regarding the use of a hearing aid the most suitable and realistic option.