Related Clues:

• Cause of a class struggle?
• New driver's hurdle
• See 80-Across
• Tough time
• Academic challenge
• Class act
• Trying experience
• Put through the paces
• Take it to make the grade
• Measure of skill
• Final, e.g.
• You need it to make the grade
• Determinant
• Kind of tube or case
• Entrance requirement, sometimes