Index and Match to find a row header that aligns with variable in specific column

I have been trying to solve this issue, but I need help:

I want to lookup a percentile that matches a certain test score of a student in a certain grade, in a score table.

So the known variables are GRADE LEVEL (Column headers Kinder-gr11), and TEST SCORE. step 1: lookup the grade level of a certain student, step 2: lookup the test score of this student, step 3: result is the matching percentile score (row header).

I cannot get this to work! So frustrating. Here is a sample Google Sheet: https://docs.google.com/spreadsheets/d/1s9Z8OBOg4ibt73Ppk3wn9wHedi_U8_stL9lf1GCQQ9g/edit?usp=sharing

Anyone have ideas?

Thanks, Hans