What is the highest map score for 8th grade?

There's no single "highest map score" for 8th grade. MAP (Measures of Academic Progress) scores are relative, not absolute. They depend on the specific test version, the student's grade level, and the test's norming group. A score is interpreted in terms of a RIT score (Rasch Unit), percentile rank, and growth. There's no single maximum RIT score; higher RIT scores simply indicate higher achievement compared to the norm group.