They won't let Americans in, except during the mas games, and even otherwise you can usually get in with a Chinese tour group. One of my American coworkers in Beijing went back in 2011 or so, and didn't have any problem, although I got the feeling it wasn't as interesting as she thought it would be.
Educationally speaking, the DPRK would catch up pretty quickly if they were able to liberalize their economy as much as China, even without all the help they could get from ROK, Japan, USA. It isn't Afghanistan (where liberalization wouldn't stick), or even Laos where there is a lot of work to do on modernizing society, which makes its current state even more depressing.
IMO NK in the unfortunate geographic situation where Kim's inherited the half of the peninsula with just not enough ariable land, but not so not enough that juche isn't viable. NK with water access could probably be an alright middle (or even upper middle) income country exporting their 5-10T mineral reserves. They had enough prexisting/rebuilt industry to perhaps even export higher value processed goods + not unserious effort at socialism to avoid dutch disease. Kims playing a solid hand poorly, but the cards are still enough not to fold. Which is sad.
Educationally speaking, the DPRK would catch up pretty quickly if they were able to liberalize their economy as much as China, even without all the help they could get from ROK, Japan, USA. It isn't Afghanistan (where liberalization wouldn't stick), or even Laos where there is a lot of work to do on modernizing society, which makes its current state even more depressing.