Synonyms of underachieving

1 Syllable

slow, dim, dull, weak

2 Syllables

dummy, numbskull, simple, dumbbell, backward, stupid, gorked, dumbo, dopey, touched, sappy, yo-yo, pinhead, dumdum

3 Syllables

birdbrained, slow-witted, retardo, subnormal, dim-witted, retarded, moronic, half-witted, opaque

4 Syllables

lamebrained, imbecile, defective, exceptional, feeble-minded, simple-minded