GOD'S WORD® Translation
Then the disciples came to Jesus privately and asked, "Why couldn't we force the demon out of the boy?"

American Standard Version
Then came the disciples to Jesus apart, and said, Why could not we cast it out?

Berean Study Bible
Afterward the disciples came to Jesus privately and asked, “Why couldn’t we drive it out?”

Douay-Rheims Bible
Then came the disciples to Jesus secretly, and said: Why could not we cast him out?

English Revised Version
Then came the disciples to Jesus apart, and said, Why could not we cast it out?

King James Bible
Then came the disciples to Jesus apart, and said, Why could not we cast him out?

World English Bible
Then the disciples came to Jesus privately, and said, "Why weren't we able to cast it out?"

Young's Literal Translation
Then the disciples having come to Jesus by himself, said, 'Wherefore were we not able to cast him out?'

Matthew 17:19 Additional Translations ...