Final answer:
Providing differentiated instruction that builds on students' unique strengths and experiences is the best way for an elementary school principal to address the situation of certain student groups performing at lower levels.
Step-by-step explanation:
The best way for the elementary school principal to address the situation of certain student groups performing at lower levels is to provide teachers with professional development aimed at providing differentiated instruction that builds on students' unique strengths and experiences. This approach recognizes that students have different learning needs and styles, and teachers can tailor their instruction to meet those needs. By incorporating strategies such as flexible grouping, using diverse instructional materials, and implementing student-centered activities, teachers can effectively support the academic success of ELLs and economically disadvantaged students.