Apparently, these batteries can be a bit finicky. We'll try our luck in class and see how it goes!
Update: We did successfully make the batteries in class, and were able to measure voltages of about 0.9 V per lemon. However, this was not enough to light up an LED, especially since more current was also needed. Later, by attaching three lemons in series, and making three sets like this, then attaching these three sets of three lemons in parallel, we could finally get enough current and voltage to make an LED light dimly.
Update: We did successfully make the batteries in class, and were able to measure voltages of about 0.9 V per lemon. However, this was not enough to light up an LED, especially since more current was also needed. Later, by attaching three lemons in series, and making three sets like this, then attaching these three sets of three lemons in parallel, we could finally get enough current and voltage to make an LED light dimly.