First Day Jitters by Julie Danneberg (2000)
Everyone knows that sinking feeling in the pit of the stomach just before diving into a new situation. Sarah Jane Hartwell is scared and doesn't want to start over at a new school. She doesn't know anybody, and nobody knows her. It will be awful. She just knows it. With much prodding from Mr. Hartwell, Sarah Jane reluctantly pulls herself together and goes to school. She is quickly befriended by Mrs. Burton, who helps smooth her jittery transition.