So, since we all know that all kids are the same, at what age did she become better at this?
Realistically, I think just experience with this kind of problem will help - I'm sure he'll adjust to the new and different expectations after a little while.
IME, they don't do much for the noise they most need to block (but, I only tried them out in the store).
The problem persists, but she has learned some ways of dealing with it and is learning more as she matures. When she was younger I was the one determining a rest break (momentary or longer) was needed, and how that rest break would be spent. ("Okay, sunshine break for 10 minutes, then we will try this again. You can run around, swing, sit, whatever, but be in the sunshine and fresh air until I tell you 10 minutes is up." Though sometimes I follow my gut and let them stay out a while longer if I thought it was doing them some good. Or if I wanted more sunshine for myself.) What worked best break-wise was at least 5 minutes of a complete change of scenery, requirements, and expectations. Just for those break minutes. And I didn't allow the break to be spent plugging oneself into a device. It had to include some physical movement, though that movement didn't have to be strenuous or take up the whole 5 minutes.
I had to be the one to determine the need for a break when she was younger because she simply couldn't. (Sometimes she still needs someone else to suggest she take a short break.) She might request a break when faced with something she simply didn't want to do, but when she truly needed a break she couldn't think of doing this. (Sometimes I granted requested breaks before tackling a tough task, but I kept them short so we wouldn't lose focus.) She also found it especially distressing that her younger sister never seemed to struggle in the same way, which added further to her distress.
As she has gotten older and shown more inclination and ability to self-start on various things I have allowed her to drive her study schedule a bit more, with check-ins and some topics still driven by me. It can still be a struggle for her, and I have to remind myself that she was diagnosed with a very short attention span (among other things), and she and I are working together to find ways for her to learn to eventually self-manage this on her own as an adult. We take it in stages. If a step we attempt is too hard to reach at the moment we look for a smaller step and keep going.
Exposure to new problems/things to learn and practice with them do help over time, but the trick, especially whenever faced with something new and daunting, is to find ways to get through it without it being so tortuous that she decides it's hopeless, worthless to try, and feels that she is simply stupid in this regard. When that mindset sets in learning the stuff becomes impossible, and I find we have to step away from it for some weeks, at least, and try returning to it later.
One interesting thing I realized as I was reading through Fluent Forever was that the Spaced Repetition System he talks about in the book (not something the author "invented", SRS is widely used in a lot of fields of study) is actually something we have stumbled into in bits and pieces over the past few years. As we work through this year and DD16 uses this in her French studies we can look at how it might help in other studies, too. SRS may prove to be a very valuable study tool. (The Anki Slashie keeps promoting is one digital application of SRS. DD16 will be using Anki, Slashie!)
When we switched to homeschooling I realized I didn't know all of the subjects my kids would need to study, so I determined I would learn alongside them for such topics. What I didn't realize is that the biggest part of my education is learning how each of my kids in particular learns best, what their strengths and weaknesses are. I had to drop my expectations of how kids should learn because those were based upon my own memories of when I was a kid, how I learned best. This simply didn't match DD16 at all, and while DD13 matches my style more closely she also has some distinct differences from me.
Hang in there. Pay attention to what does work, and when something doesn't work as expected examine the situation to see if it simply requires a break to freshen brains or if a slight change in approach might help. Every person is different, and kids' brains mature in stages. Sometimes the stages of brain maturity don't always follow one set order, so it takes some discovery (largely through observation and trial & error) to figure out which segments of brain function are where maturity-wise.
Also remember that allergies and other environmental factors (barometric changes for me has always been a biggie) can affect performance, too, causing the brain either to leap forward on stuff on a particular day, or to seem to regress and forget stuff you thought was cemented. Roll with it. Alter the day's plan if needed, and focus on the stuff that is coming more readily. If the brain can't work at all on studies it could be a good day to tackle physical work, perhaps decluttering clothing, books, toys (removing outgrown things) and generally cleaning up.
Sorry this is so long. Every child is different, but there are some similarities at times, and sometimes hearing what someone did for their kid can give one ideas to try, things to think about when trying to help their own. I hope the above contains something helpful for you, but even if it doesn't please know that I am rooting for you and your sons. You'll figure it out, so hang in there.