Drill through

Hi everyone.

I have a school report.

I have a clustered bar chart with grades per subject. 

I have Y axis: Subject name and X axis: grades (above/at/below..)

I have created a drill through to an assessment page with a table. Im not able to select a specific grade from a specific subject.

I have created a slicer to filter the grades and it shows the specific grade on the visual but when I drill through it still takes me to the page with all kids and all grades for that subject. Its like the drillthrough is only considering the subject.

I am looking to select a specific single bar within a subject and drill through to the page where I will see that specific cohort ONLY.

Any suggestions? Help required urgently as I have a meeting tonight where I am presenting this data.

Thanks