My suggestion does not respond to your concentration question, but thought I'd share something that helped me study for tests. I had a full-time job, married w/1 child when I went to college, so very busy with lots of interruptions..

I would purchase a spiral bound set of index cards. I would basically use them as flash cards. Ex: Geology. On one side of a card I'd write "igneous rock" and the other side "Rocks formed by the cooling and solidifying of molten materials. Igneous rocks can form beneath the Earth's surface, or at its surface, as lava." and so on, depending on the subject.

I would then carry it with me everywhere. I'd pull it out and read it during traffic or sitting in a long line at the fast food restaurant, etc.

This won't work for some subjects but will for many. That study technique helped me squeeze in studying in small blocks of time.

Hope this technique helps some study, as it did for me.