Formative Assessment during Design Labs

Check-off Points

Check-off Points

“Check-offs” are particular points in the lab where we say to students, “Okay. You’ve now done all this work. At this point, you should be ready to have a discussion with the teaching staff about key concepts.” We basically conduct a brief and informal oral exam with them. It’s also an opportunity for the teaching staff to make sure the students have built their circuits correctly, because they’re going to use them for the entire lab. At the end of the check-off, if the staff member is satisfied that the students understand the material, he or she electronically records that the students have completed that particular part of the lab. The check-offs are not graded, but their completion does count toward students’ final grades.

“Check Yourself” Questions

"In the design lab, students are always thinking, working, and being active—and the teaching staff is available to help them at all times."
—Sanjoy Mahajan

Between one check-off point and the next, there are four or five “check yourself” prompts included in students’ lab instructions. These are questions that prompt students to assess their own understanding. When one of the teaching staff comes to do a check-off with the students, we go through all of the “check yourself” questions to make sure they understand the key concepts. We also use that time to teach them content they weren’t quite able to learn working by themselves.

Anticipating Misconceptions and Adjusting Instruction Prior to the Design Lab

Once a week, all the teaching staff members meet together to do the lab work that will be featured in the upcoming design lab. This meeting is important, because, in order to conduct productive check-offs with students, you need to have done the lab yourself and to deeply understand the questions. During this pre-lab session, the teaching staff members who have already completed the lab several times during earlier iterations of the course act as the core instructors and give the new instructors, who act as students, check-offs. The idea is to teach these new instructors what they should be looking for when they give check-offs.

This practice allows me to anticipate students’ misconceptions and adjust instruction prior to the design lab. For example, in one of the labs, there was a circuit exercise that asked students to drive a Lego motor with a variable voltage, in preparation for building a circuit that enables the head of the robot to track light. The first step was to build a variable voltage with a potentiometer (a variable resistor). As the new instructors varied the resistance during the pre-lab session, they correctly got different voltages. 

But when they attached the motor to the variable resistor, the motor wouldn’t turn on. The goal was for them to see that when you have this 10-kiloohm resistor, and you attach a 3-ohm motor, it creates a short circuit.

We asked the new instructors to make a table of the estimated voltages at four positions of the potentiometer. The undergraduate teaching staff just refused to do it properly! They wrote a ream of equations and got totally confused. Then they graphed the equations with a symbolic-mathematics tool like Mathematica, but still did not understand the key concept—which is that for almost all positions on the dial, the motor resistance is so much smaller than the variable resistance that no voltage appears across the motor.

As a result of this experience, I changed how we taught the lab with students. Specifically, we prompted students to estimate their values within half a volt. Once you do that, all the answers are zero, except the last one, which is ten. Then, instead of prompting students to do many different values of the dial setting, we asked them to do just three, and then to do one in reverse, with the idea being that they could easily graph those values.  But instead of graphing the values by hand, students still used a computer and developed no understanding.

Even this intervention didn’t help enough! I received feedback from another instructor that students still tried to solve the problem using algebra. So at the beginning of my design lab, I said, “We’re going to talk about this problem. I’m going to teach you some things about approximating resistances with series in parallel that will help you with this part of the design lab.” We did quick conceptual questions until everyone was at a level at which they could understand the key concepts. This worked well! By the time they got to the check-off junctures, many students had solved the problem with understanding and all were at least attempting to approach the problem productively. This meant that during our work together I could help them understand the content, instead of simply redirecting their efforts.

Learning Resource Types
Lecture Videos
Recitation Videos
Problem Sets
Exams with Solutions
Lecture Notes
Instructor Insights
Programming Assignments