Answer:

EFS

Answer	Crossword Clue
EFS	Scruffy pair?
EFS	Daffy duo?
EFS	Gees' predecessors

EFS	Letters
EFS	Fluffy's threesome
EFS	Two of fifteen?
EFS	Abysmal grades
EFS	Marks of failure
EFS	Reasons for repeats, maybe
EFS	Fig leaf's outer edges?
EFS	Affair twosome?

EFS	Affluent couple?
EFS	Pair in Banff?
EFS	Report card calamities
EFS	"Fluffy" threesome
EFS	Fluffy trio?
EFS	Jeff has two
EFS	Poor grades
EFS	Bad grades

EFS	Flunking letters
EFS	A lot of fluff?
EFS	These are no passing fancy
EFS	Report card disasters
EFS	Waffle center?
EFS	Scruffy couple?
EFS	Gee preceders
EFS	Terrible grades

EFS	Puff pieces?
EFS	Letters of the alphabet.
EFS	Letters.
EFS	Failing marks.
EFS	Grades that don't make the grade
EFS	Trio in fluff
EFS	Failing grades
EFS	4-point Scrabble tiles

EFS	Awful grades
EFS	Letters starting many military plane names
EFS	A lot of fluff
EFS	Two of fifty
EFS	40% of fifty?