At least since the early~80s there have been researchers and teachers claiming that understanding concurrency is a necessity for our students. Many authors also write that concurrency is very difficult for students to learn. However, other researchers claim that concurrency is something natural to most humans and the problems are caused by the way we teach the subject and the languages/tools we use.
This paper looks at a number of articles that discuss concurrency and student learning. Many of them discuss various tools, sometime without giving any evidence that they solve a problem that students actually have and/or that the tools improve the situation. Others discuss course designs, where the designs are based on assumptions about how concurrency should be taught. There are also studies that try to understand what causes the problems that students experience and how to improve the situation.
Unfortunately, in reading these articles we have to come to the conclusion that the situation today is much the same as in the early-80s: We do not know how to teach concurrency.