Still not sure how to teach

Today is week 5 of the Elektronika Dasar class that i teach. We've finished discussing diodes 2 weeks ago, so I decided to give the students a quiz (without telling them beforehand).

And the results were almost as predicted: unsatisfactory.

I made it my intention to test them with simple questions but with slight "twists".

Question number one was about the basic rectifying behaviour of diodes. (21 answered wrong, 24 answered right)

Question number two was about zener diodes. The circuit topology was made exactly the same as in a previous assignment, but as I had suspected, not much of them really understood what they handed in. Only six students answered correctly in the quiz, while almost ALL OF THEM answered right in their previous assignments. Amazed? LoL.

The last question was a "twisted" version of a clipper diode. Instead of giving an output as a clipped version of its input, in this question I wanted the students to draw how to put a protection diode that can clip the input to a certain voltage (Vcc=5V). Only a few answered the right answer, but I admit for this question it might be a bit too hard to come up with the "expected answer".

Anyways, the bottom line is that it's very important to accurately know how the students are doing in a big class, and this can be done by giving assignments and quizzes, and teachers SHOULD evaluate the results ASAP (never postpone marking assigments to after exams... never!). It's one good way of getting feedback.