I was not in the GT program in elementary or middle school (high school didn't have one). In theory, I should have been no question, but I was a poor student. I wasn't dumb at all, I was just
really lazy. I loathed homework assignments of any kind. I almost never did them unless it interested me or on the spur of the moment decided to do it out of necessity (i.e. getting in trouble). As such, my grades suffered a lot, and in my 1st to 7th grade school district (I moved to a different county for 8th to 12th grade) they put A LOT of emphasis on home work, studying, etc. which is not what I needed or wanted. In my mind, school was for school, home was for home, and they should not mix.
I had lots of tests preformed on me when I was young because I had behavioral problems and "marks of genius" in class, but without the grades or apptitude to support it. They wondered if I had learning dissabilities, wasn't challenged enough, challenged too hard, and everything in between. The reality? I hated in-between work (to this day I still do). I would see the end goal of what needed to be done, and just wanted to get there by my own means. In 4th grade they did a most of the tests on me, and my mother was told that they so badly wanted to put me in the GT program (my math skills were apparently at a 9th grade level for example), but they couldn't because I was lacking in english/reading skills (that was a product of laziness, I just didn't give a shit about it as I found it profoundly boring) and couldn't get my act together. I never did either.
A lot of why this happened is my thinking style. I am a conceptualizer. I'll usually intuitive figure out how something works but lack the in-between tools process to make it through it without assumptions/guesswork. This is why my math skills tested so high. The problems weren't so much of "solve for x" but the thought processes of how one needs to think through things. Because of this nature of "figuring things out", I would sit in class and just get something, it would make sense to me and I'd write it off as me knowing it without practicing or working at it. The problem is I wouldn't make it all the way with everything, and when it comes to the basics you have to practice. When I would try and something wouldn't come as easy as it did initially, I would get VERY upset with myself and prefer to quit. I didn't want to have to be faced so close with my own incompetence, so I preferred to ignore it. What I needed was the correct encouragement to use my talents. As opposed to being stuck in a system that just didn't work for me. I ended up failing reading in 7th grade (for different reasons from what I described above) largely out of a buildup/pattern of ignoring things I disliked, using my social/lying skills to spin stories so I didn't have to do homework and projects. I got so used to it became an automatic habit.
Once I got to 8th grade though things started to turn around. Different system, teachers that fit me and made a point to work with me and not judge based off my crappy history, and ultimately just a reset button that does WONDERS for me. I started to prove myself that I started high school in remedial english (below basic) as a freshmen, to advanced english my senior year. I also took two math classes my sophmore (geometry and algebra II). I was put into average level geoscience at the very beginning of freshmen year and was very upset (I wasn't perfect in 8th grade, I was about 75% where I needed to be), and raised hell demanding to be bumped up a year. Long story short I got put into biology after a few weeks, got to honors levels for sophmore, then took both AP chem (got a 5) and honors physics junior year, finally I took AP bio (got a 5), AP physics (this was dumb, they only offered the B class in my school, not the C. Thought I'd try the C test and ended up getting a 1

), and an independent study in organic chemistry my senior year. I ended up winning the award for the most outstanding senior in science by a landslide. When I informed my teachers of where I was at and what I was like when I was young they were very surprised.
When I reflect on the huge leaps I took in high school, I simply needed a different system. They were right, I was GT material early on, I just didn't have the right conditions or mental facilities to handle it (aspergers syndrome being a major factor). Over christmas this past year when I was visiting my hometown, I stopped by my old elementary school to see some old teachers I haven't seen since I was 15 or so. What was interesting is several of them said they knew I would "snap out of it" eventually, and weren't worried. That it was just a "maturity issue". Ultimately, the fact that those comments were rather universal makes me wonder if GT would have boosted me at all. I ultimately rose as high as I could as far as level goes anyway. I think most of what it would have taught me would be better work ethic and not to knee jerk react to difficulties. Though I have to admit, those things would be really really useful.