Practice
Lab work is important. It is important to make students practice what they learn. It is not enough that a student understand and know a concept or skill. Actually practicing the skill provides the learner with mastery of the skill and builds more confidence in using it. Without practice a student would probably get stuck in the real world when he attempts to use the concept or skill he thought I had learnt. As new concepts are introduced, old ones may get buries. Practicing new concepts as they come out helps strengthen them in the mind and counteract such burial effect.