I am from the old-school. Seldom used a calculator and, to say it all, I never "trusted" that much a calculator's answer..
I do a lot of math in my head. Usually, you only need an approximate answer, and I can usually find an approximate answer faster in my head than on a calculator. I almost never do arithmetics on paper, although I do use paper for algebra.
Today I am an ex-teen ager (more or less) and my math abilities faded somewhat, but you won't believe how much I enjoy helping my son with his homeworks..a good excuse to listen to some AC/DC tracks while letting my writing hand fly on paper!
I know the feeling. I've helped my step daughters and the the eldest girls boyfriend with high school and university (or, rather, the Swedish equivalents, as we cut the line between high school and university a little differently) maths, and it has been very rewarding. It's been fun seeing them grasp "math as a language" and get a feel for it. It's also been very developing for me. When I went to school som 25 years ago, I just learned "how" and pretty much skipped the "why", because that's all that was needed to ace the tests. However, as I helped them, I realized that, from the experience gained by using the math over the years, I've also gained an intuitive understanding of the "whys".
However, helping them also gave me a deep hatred for math book authors. Seriously, math books are the most un-pedagogic crap you can find. Some are better, some are worse, but I've yet to see one actually reach "acceptable". When teaching advanced math, the most important hurdle you need to get the student over is "Why is this important for me? When will I ever have any use of this?". It's by far the most common problem, the student fails to see the relevance, and thus fails to muster interrest in the subject.
So, how does the authors handle this?
They don't. They are usually the kind of mathematician who somehow thinks that "Real world examples sullies their nice, clean math". Seriously, they are about as useless as a car mechanic who doesn't want to get his shiny tools dirty. If there are any real world examples, they are usually token examples thrown in at the end of the chapter, and so abstractly unpractical that they only become ridiculous. They totally fail one of the three basic rhetoric pillars, ethos (why is this important to me?). I could easily come up with dozens of real world examples that feel real and relevant, which were much better than the ones in the books.
Also, when the books explain something, they tend to do it halfway, which just leaves the reader confused. I could "decode" it with my math skills, because I've already knew it, but if you don't already understand what they were trying to explain, it's more or less unintelligble.
Seriously, I almost considered writing a better book myself (perhaps with a little help from a mathematician friend).
Still, that said, help kids with math. It's really rewarding on so many levels.