Level 1: Reaction
You want people to feel that training is valuable. Measuring how engaged they were, how actively the contributed, and how they reacted to the training helps you to understand how well they receive it.
Level 2: Learning
Level 2 focuses on measuring what your trainees have and haven't learnt. Level 2 also measures what they think they'll be able to do differently as a result, how confident they are that they can do it, and how motivated they are to make changes.
Level 3: Behavior
This level helps you to understand how well people apply their training. It can also reveal where people might need help. But behavior can only change when conditions are favorable.
Level 4: Results
Analyze the final results of your training. This includes outcomes that you or your organization have decided are good for business and good for your team members, and which demonstrates a good return on investment (ROI).