Let your students know that their sketch doesn’t have to look exactly like the object in front of them. It’s just a sketch!
For example, if they were referencing a bottle that has a label on it, have them go in and add the label and any text on it.
For example, if the light source is a lamp shining directly down on the object, your students would draw a circle or arrow at the top of their paper to indicate that’s where the light source is.
For example, you could say to a student “Nice job, I really like how you shaded this drawing. Is there anything you would change or do differently next time?”