You bring up two points here that are usually the cornerstones of my arguments. The first, the coloring; I have witnessed a "test" like this before, where a child was given a pack of crayons and a picture to color. The child scribbled and drew random lines and went all over the page. The parent said "See? He can't even focus enough to color a picture". The doctor then asked the child "Why did you color the page like that?" and the child replied "I liked the way it looked, and I didn't want to color that picture". What the parent was mistaking for ADD was, in this case, just the child "expressing his self artistically". When the doctor asked the child to color within the lines and make a nice picture for his mom, this child was able to do so, without issue.
Children express themselves in varying means and to varying degrees. A child who constantly asks "why" isn't starving for attention or trying to "embarrass mommy", the child is merely trying to express an interest in his/ her surroundings and is vocalizing that interest in the only way possible. The problem comes in with parents who can't be arsed to teach their kids things, or to answer the "why" question because they're too busy texting their friends and trying to hold on to the last desperate piece of youth.
Second point: the public school syndrome. In this day and age of "no child left behind" teachers are faulted for the poor performance of students, even if the poor performers are in the minority. Teachers are forced to cater to the lowest common denominator, and the kids who understood the concept on the first or second go-round are left to fend for themselves while the "slow learners" (I'm using this term loosely, because EVERYONE has a subject which takes a little more time to learn; I'm not singling out "stupid" people, I'm talking about the kid who just doesn't seem to grasp the concept) get the individual help from the teacher. Now-a-days, teachers fear having to send a child away to a learning specialist, because the child will usually go home with the story of how Miss So-and-So wouldn't help me learn, and now you have a furious parent to deal with.
No... teachers don't want to hear you complain about how they refused to help your child understand fractions, so they help the slower learner, leaving the ones who caught on to fidget, talk, and drift away from the conscious learning environment. Then, when Parent-teacher conferences come along, Miss So-and-so has to explain why little Brian "is a bright student and extremely smart when he applies himself, but has a hard time focusing". Little Brian's parents want to know if something is wrong, take him to the doctor, describe the "symptoms", and of course, Little Brian has ADD. Have some Ritalin and it'll be all good. Multiply scenario by 30 kids per class, 2 classes per grade, 6 grades per school, and 5 schools per city... "As of 2007, 2.7 million youth ages 4-17 years (66.3% of those with a current diagnosis) were receiving medication treatment for the disorder." http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5944a3.htm?s_cid=mm5944a3_w
That's not to say the condition does not exist; it most certainly does. I'm not quite sure how to classify it, in terms of where the disorder manifests itself (psychological, physiological?), or if we're really just lumping several disorders under one umbrella (similar to Autism, as recent as 10 years ago). The true-to-life cases need to be observed and treated. The not-so-clear-cut cases need to be weeded out and given help. The parents who would rather medicate their children then answer "why"... well, I'll leave my opinion of them to your imagination.