How do I prove that people actually learned, not just attended?

You have raised your own bar. You are no longer content to fill seats, you want real understanding, and now you are stuck on the hardest part: showing it happened. That struggle is a good sign. It means you are measuring the right thing, even though the right thing is harder to measure than attendance. Understanding shows up in behavior, not in a sign-in sheet. People who truly learned do something differently afterward. They solve a problem they could not before, explain the idea to someone else, make a better call on the job. Those are the traces to look for, not just a quiz score the day of. So pick one skill from your next program and follow it past the room. Ask managers or the learners themselves, a few weeks later, whether anything actually changed in how they work. Start with one thread, not everything at once. Proof of learning is built from watching what people do differently, and you are already asking the question that gets you there.