Unfortunately, I believe that many do. Most teachers are not trained to see the signs of giftedness in students and sometimes they can be difficult to identify since they are as diverse from each other if not more diverse from each other than the general population. Most teachers don't have a degree in gifted education nor are they even aware of what a gifted child really is. If you ask many teachers who the gifted kids in their class are they'd likely say the ones who are always attentive, gets straight A's, abides by the rules, etc. The truth is that this description couldn't be any more wrong. Gifted students are most often bored in a regular classroom and may have behavioral issues in class. They generally don't make straight A's and get frustrated with the standard classroom. Most teachers are able to see signs of those that are struggling, but they don't recognize that the unusually intelligent need assistance as well. 33% of the American education system's budget goes toward helping children with the "typical" special needs, and only 1% actually goes towards gifted education, but this is a special needs population as well. Many gifted students can become underachievers and even drop out if they don't get the help they need to fulfill their potential. Gifted students aren't your typical wonder students and some can actually be learning disabled as well which makes it even more difficult to identify a gifted student. Gifted students with a learning disability are known as "twice exceptional" or "2E."

It's not necessarily that they go unidentified, from most of the gifted people I know, we just don't make it obvious. And iq tests are based on the person's ability to learn, not how intelligent they are. If you were a great learner but had test anxiety, this type of thing wouldn't show in grades alone.