I've been to CalcII and have my BS degree in Biology graduating with a 3.9, but I still cannot do even the easiest math in my head. I am not defending Weingarten at all, just saying that some of us cannot "do math" in our heads. That limitation caused me many years of a college education because I truly felt inadequate in that area.
My high school geometry teacher actually told me that I would make a better stripper than a college student. Thank goodness I didn't take that as true, but it did cause me to go many years without an education in an area that I really loved.
One reason I can't do math in my head is that my brain will reverse numbers...calculators have been the BEST invention. I know and understand the theory, and can work a problem, but either along the way or with the answer there will be a numerical reversal making the problem wrong. I will even verbally say the correct number then write the number incorrectly. But with a calculator, seeing the number somehow allows me to then write the correct answer.
So to make a judgment on someone based on that one example is quite unfair. I too, am quite skeptical of teacher unions and the people who staff them; however, I am even more skeptical of those who would so easily jump to judgment.
But, you're not a teacher, and not the head of a union, whose members are generally regarded as unqualified for the job.