Does sentence mining actually work?

Yes, sentence mining works, and the reason is simple: learning a word inside a whole sentence gives you its grammar and its context at the same time, which sticks far better than a bare word-to-word pair. Add spaced repetition and you keep what you mine. It isn't a trick. It's two well-supported ideas doing their job together.

The first idea is context. A word you learn from o comboio das oito esta atrasado arrives with its article, its verb, and the moment you'll use it, so you recall it the way you met it. A word off a list arrives naked, and you freeze when you need it live. The second idea is timing: spaced repetition shows a card again right before you'd forget, so effort goes only where memory is about to slip. Both lean on Stephen Krashen's point that we absorb most from input just past our level.

The honest catch isn't the method, it's keeping it up. Mining cards by hand is a couple of minutes each, and most people quit after a fortnight of tab-juggling. So the real question is which tool keeps the habit alive. If you want the mechanics first, we walk through the whole method.