Write down some performance targets before training starts.
Assign a homework problem at the end of each (hopefully short) training session. Evaluate performance on each one, including elapsed man hours to complete the assignment. Measuring this may be simpler if we expect work on the assignment to begin very soon after receiving the assignment.
When observed performance exceeds your written goals, truncate or halt training, as your students are now ready to apply what you taught.
Training a new cohort will be easier to plan, as you’ll be able to rely on past experience.