Here is how the words should be sorted:
1st syllable:
frighten
ninety
higher
driveway
slightly
lightning
sidewalk
highway
brightly
2nd syllable:
polite
delight
surprise
decide
advice
survive
combine
arrive
provide
invite
describe
tonight
Oddballs:
(These words are oddballs because they look as if they have the long -i sound in the 2nd syllable, but they do not.)
machine
forgive
favorite