For me it was especially frustrating because I feel as though there were a lot of signs that my parents ignored in me but noticed in my older brother.
While he was given tools to work with his problems I was not. He was given a therapist, medication, and a tutor. It was at a time when boys were the focus of ADHD and nobody ever brought up that I might have the same issues as he did.
A lot of my early school experiences were typical of a girl with ADHD at the time (early 90's)- the solutions teachers had were ineffective bandaids that assumed I was intentionally disrupting class.
I had a teacher in first grade who impacted me negatively for a long time- she didn't know how to deal with me in class (I was exceptionally disruptive and in her defense she was pregnant with twins) and so she had me placed in remedial courses which took place during the normal school day--- these courses were meant for children who could not read or had other issue like speech or dyslexia---not for children with ADHD or other behavioral issues. It absolutely killed my self esteem- I was bored and felt isolated, but I believed it was my own fault and if I could just be "good" I wouldn't have to go to the "special" classes anymore. I was punished by teachers for something I couldn't control. I sat in a dark room with a teachers aide and other students while we went over how to pronounce R's and W's and differentiate between H versus N on on paper.
There was also a music teacher I had in elementary school who told me if I could sit the whole class without talking or squirming I would get a prize - I tried so hard every class but I never got the prize- he made it a big thing in front of the other students and it made me feel singled out and awful. My teachers didn't know how to deal with me, and I didn't know how to deal with me- I internalized the negativity for a long time and was convinced I was an unworthy person.
I was diagnosed after I graduated high school (I ended up getting my GED during the last semester of my senior year, but that's another story). I was given a series of tests by my psychologist where he determined I had a higher than average IQ but essentially the attention span of a 3rd grader. I was prescribed Vyvanse and it was like the world became clearer over night- with the fog mostly gone I think it's the first time I had confidence in myself and my ability to be a functioning person.
I've been medicated now for about 5 years and while I still struggle, knowing what is wrong means I'm in a better position to address my problems effectively. Diagnosis makes a world of difference.