What should be the school leader's most appropriate action for improving Ms. Thompson's practice after the testing error?

The most appropriate action for improving Ms. Thompson's practice after the testing error is to provide her with immediate targeted training on professional ethics. This choice emphasizes the importance of understanding the ethical considerations related to testing practices, especially in light of a significant error that may impact student outcomes and trust in the educational system.

By focusing on professional ethics, the school leader can help Ms. Thompson gain insight into the responsibilities associated with administering assessments, such as ensuring fairness, accuracy, and transparency in her evaluation methods. This tailored approach directly addresses the root of the issue—understanding and upholding professional standards during testing—thereby promoting better practices in the future.

The other options, while beneficial in their own contexts, do not specifically target the immediate need following the error. Conducting a workshop on assessment strategies might enhance Ms. Thompson's overall assessment skills but may not directly address the ethical implications. Implementing a school-wide review of testing materials could result in a better overall process but may not provide the individualized support Ms. Thompson requires. Offering tutoring for students who performed poorly addresses student needs rather than addressing the teacher's practice directly and does not help prevent future errors. Thus, immediate training on professional ethics is the most focused and relevant action following the incident.