Mrs. Boone has been teaching sixth-grade Science for five years. She is very knowledgeable about both the state standards and the content of the course. She has excellent rapport with her colleagues and is active with her school’s extracurricular activities. However, she has noticed some undesirable behaviors occurring during her instructional blocks. Many of the students begin socializing during extended lessons and independent work. Which of the following behavioral strategies would be most helpful to Mrs. Boone in reducing the students’ socializing and time off task?