It's fairly common for parents, especially first-time parents, to have no real idea of what "normal" is for a child of their kid's age. This guide is written as a "translator" -- a way of using the words a teacher might be using to describe your child's behavior to understand your child's brain. Teachers often hesitate to label a student with ADHD -- in some states, they're legally not allowed to -- which means, as the parent, the responsibility is on you to recognize it when it's described.
The Teacher Says: "Your Child Doesn't Complete the Work"
Ask your teacher: why not? If the teacher describes a series of situations in which your child got absorbed by a non-work task and forgot that the assignment existed, consider the potential of ADHD to cause that kind of distraction. If the teacher describes your child getting frustrated that other children were being noisy or disruptive, or simply staring out the window rather than finishing up, you might have a child who really wants to do the assignment, but literally can't.
The Teacher Says: "Your Child is Always Talking"
If your teacher complains that your child is constantly interrupting the person who should have the floor, or that they cannot seem to keep quiet during quiet time, consider the potential of ADHD to make them forget the 'rules' of school conversation. Kids with ADHD often blurt out their thoughts without a filter. If your teacher complains that your student takes a lot of words to get to 'the point' when answering a question, that's also a classic sign of ADHD.
The Teacher Says: "Your Child Doesn't Get Along"
Ask your teacher: when? Often, children with ADHD have troubles dealing with frustration when they don't get what they want, and they frequently feel like they must have the last word. This can lead to some amazing screaming matches, but also to some completely failed attempts at cooperative time. If they get along when not 'in the spotlight,' but not when their performance is being deliberately observed, ADHD is a strong possibility.
The Teacher Says: "Your Child is Never Paying Attention"
If your teacher complains that your child asks "what?" or other simple, broad questions even when they appeared to be listening -- or acts like they understood but then clearly had no idea what they were supposed to be doing -- that's an excellent indicator of ADHD. Children with ADHD are often smart enough to present the right appearance (i.e. of listening, or of understanding directions) even when their brains are actually busy building Minecraft buildings instead of listening. But when the time comes to display their understanding... it's just not there.
Understanding how a teacher sees a student with ADHD -- whether they recognize it or not -- can help you understand precisely how and why your student might need some well-deserved help to 'make it' at school. The worst thing you can do is force them to continue to fail when the potential for them to thrive is just an open acknowledgement away.