My daughter did do this in August of this year. She had just turned 13. She is not a kid who likes to spend time away from home, but she begged to be allowed to go. We live within 3 hours of DC, so we allowed her to go.
Pros- They did some really neat things, including a teambuilding day at a ropes course and a "Washington at Night" tour. They spent a day at the capitol and at one of the Smithsonian Museums.
My daughter met kids from all over the United States, although she didn't really connect with them at first (very shy). By the end of the week she was having a better time.
It looks good on a resume.
Kids were staying in a hotel. JNSLC staff was posted on every floor throughout the night, and those kids couldn't even poke their heads out of their rooms without being caught - in other words, night time supervision was very strict, which was a good thing. They had a curfew, and if they were being loud in the rooms after curfew, they were told to knock it off and go to bed.
The group leaders were young and enthusiastic. My daughter had a young man in his 20's leading her group, and she said he was really good with the kids.
Cons- In addition to the field trips, which my daughter mostly enjoyed, they spent several hours a day attending lectures. My daughter said these were excruciatingly boring, and a lot of the kids napped through the lecture.
Plan on spending a bundle for a new wardrobe. My kid, who mainly wears jeans and t-shirts, had to buy formal, business and "Business casual" clothes, as well as appropriate (i.e. no sneakers) footwear. The dress code is pretty strict. They made the kids wear long pants for a daytime tour, and it was about 96 degrees at the time.
My kid is a very picky eater. She called me after 2 days crying because she was starving. I thought it was because she was being too choosy, but her room-mates confirmed that the food was pretty awful. (They were allowed to order pizza from a local place, so that's how they solved the problem.)
They discourage parents from staying at the same hotel where the kids are housed, but we went down on Thursday night and stayed until Sunday. (The program runs from a Tuesday until a Sunday.) We saw many other parents there, but parents are not allowed to accompany the children on any of the excursions, nor may they attend any of the events at the hotel conference center.
Although security was tight at night-time, there were times throughout the day when we saw kids roaming unsupervised throughout the hotel complex. They had to wear ID tags at all times, and were forbidden from going on any hotel floor but their own, but....kids will be kids you know.
There was one day when they had to get up at 4:50 a.m. (to travel to the ropes course). My kid is not an early riser, so this didn't go over real well. On the other days, they had to get up around 5:45.
The kids were put into groups that did not include the kids they were rooming with. So even though my daughter developed a good relationship with one of her roommates, they only saw each other at meals and bedtime.
My daughter is standing over my shoulder as a type this, and I asked her whether she would recommend this experience. She said she wouldn't want to do it again, but was glad she had done it once. BTW, she was in the "Life Sciences" program, which is a little different than the other programs - not quite so "politics and government" oriented.