I got a National Semiconductor Quiz Kid, the "owl" calculator with red and green eyes. I was expecting it to have an MM5799 (old COPS), but it has an MM5780, as described in the 1977 National Semiconductor MOS LSI Databook on Bitsavers.
I already had a Montgomery Ward P50 basic calculator with a MM5737, also listed in that databook. It looks like the chips are pretty similar, except that 5780 has the red and green LED outputs instead of segment outputs. The keyboard is connected the same, except the equals key on the Quiz Kid is paralleled with the minus key, and the "test" button is really the equals key. So when you enter 2+2=4 test, you are really entering 2+2-4=. So if your answer is correct, then the result is 0.
When I have time I'll decap both of them and see if they are customized versions of the MM5799 like I expect.