I used to be one such weak runner. This is how it was.
I had a limited start to running in 8th grade, although I didn't consider myself to be a "runner." 3 days of 5 we would run in PE. We started at 4 min and somewhere down the road we got up to 25min of running (and I thought that was a lot). It was that November of 8th grade that I ran my first 5k -- 31min -- I was dead tired.
So I got to high school and didn't know anything about cross country. I was doing Leadership and other such bullshit. But I had a number of friends that I made (mostly 2 or 3 years older) that were on the XC and track and told me that I was coming out for track in January. I said sure -- I had never been opposed to running.
So, at my school, my coach trained us 50wks/yr. He did this legally by have all interested sign up through a USATF club, which gave us legal protection and insurance in case something happened, and allowed us to train 7 days/wk, 52 weeks/yr.
I filled out all the club paperwork and came out the week before the actual school track practice started. I was told that I was to run a one mile time trial and that, as a male, I needed to break 7:30 in order to qualify for showing up to practice every day. I said no prob -- I ran 7:13 -- and I was working.
At this point in my athletic mindset, I thought the point of practice of to finish with it and go home. So, when my coach found that I had only completed the club paperwork and needed to fill out the info for the school, he told me to go home and come back with it tomorrow. I said sure -- I though, "Wow, that was a quick day."
I started running and doing workouts. It was obvious immediately that I had no natural speed, coordination or strength or endurance, so naturally, I became a distance runner. I remember much of my work was 30, 45 and the occasional 60min run. I really didn't take what I was doing seriously.
My first race was a 1500m at Skyline College in San Bruno -- the first time I had ever stepped on a rubber track. I saw one of teammates (who turned out to be a 4:40 miler, 53s 400m runner and 43' TJer) and said, "I'll try to stick with him." Well I hit the first 300m in 51s and it was all downhill from there. I ended up running 6:45 and felt awful. Within a few weeks, I got down to 6:15 or so (one mile).
It all changed one day when, in the middle of some repeat quarters (with girls I might add, who were also running high 5s, low 6s for the mile), I said that I had to leave early because I had to go to work. My coach's reaction was, "Turn in your gear."
I said, "What?"
He said, "If I'm going to coach you to do this, then you're going to make it a priority, so if you're going to leave a very important workout to do something else, that's fine, just turn in your gear." And with that he walked away. I was shocked. I didn't know what to do.
I showed up to practice the next day and didn't hear my name for the bus list for Saturday's meet in Salinas. I asked him why I wasn't on their, to which he said, "I mean what I say, you have other priorities, and I don't want to incourage half-assed efforts."
It was pouring rain that day, and the team just had a very short run to do. I didn't know what to do. My coach was cleared drainage holes from the railing around the track, while the team sloshed through the water, and I decided that I was just going to stay on the infield, in the pouring rain, until he would talk with me. I started sobbing because it was then that I realized how much I liked track and that I was getting better every week. A couple of teammated came over to talk with me, but there wasn't much to say.
After about 90min, he came over and asked me to talk with him as he cleared the drains. He said that in this sport you need to work hard if you want to be good, and that you can't cut your work short and expect good results. I said that now I understood that and that it would never happen again. He told me to go home and get dry because I had a meet on Saturday.
After that day, I committed myself to work harder then everyone else, that I wouldn't miss a single run or workout, especially given the fact that I lacked so dearly in talent. I ended my first season with PRs of 68, 2:39, 5:45 and 12:39. I ran all through the summer, and in my first xc season ran 20:07 for a 2.95mi course (fairly difficult). With in 2 years I had run 57.9, 2:12, 4:42 and 10:17 as well as 16:10 for the same xc course.
So, just make it clear that this sport requires consistent work if you're going to be good, and that improvements are gaurenteed if you show up and do the work (assuming the program is sound). Then it's up to the kid to decide if they want it.