Changing conditional formating criteria based on changing data

I'm an elementary school teacher and I'm trying to create a spreadsheet that will allow me to track my student's fluency based on the student's reading level. The criteria for fluency changes based on the student's reading level so I need to create a VBA that changes the conditional formatting when I change the reading level. Example: If a student is reading at a level 20 I want a red traffic light for fluency <42 WPM (words per minute), yellow for fluency 43-64, and green for fluency >65. BUT if the student reads at a level 21 I want a red traffic light for fluency <52, yellow for fluency 53-79, and green for fluency >80.

I hope this makes sense, and I am a firm believer that anything is possible (especially within Excel) I just lack the training and knowledge of how to do it. Please help!