I coach several runners about his age, and here are some thoughts for you.
First, have him run with others if possible. I don't think that any of my runners would want to "practice" running if they weren't there with a dozen of their friends. We keep everything really fun and light and the kids are too busy laughing and having fun to ever realize that they're actually training. Fun is the magic. I don't want these kids burning out by the time they're 15. With that said, many of them are exceptional and they absolutely do not want to be told to go play capture the flag or something like that. They like to train and improve. They like to compete. I have to keep them reeled in.
Most of my kids run 3 or 4 days per week, plus many of them play other sports.
A warmup is usually a half mile - mile, followed by drills and strides. Then one of these:
Moderate effort (tempo's) repeats, building up over time. They start with maybe 3 x 300m and within weeks will do 4 - 6 x 600m with a standing rest recovery. They stop when they feel like it, or I tell them to. I run all of these with them to make sure no one is working too hard. They enjoy running this pace and it does wonders for them. After, we might do some 30m - 50m repeats with the sprinters.
Easy run. We go run 2 - 3 miles easy through a local park. Many of them could go longer, but I don't see the need to push it. they finish the 3 milers happy... good enough for me. Follow it up with some 30m hill repeats.
Sometimes some 150m - 250m repeats around the effort of an 800m race pace. I have them do this as a group off the line to simulate the start of the race and learn how to get out hard and then settle in to the right pace for each of them. Long recoveries.
Occasional race. My strongest 800m runners will regularly race 100m - 3000m for variety. Whatever they want is fine with me.
No gut busting intervals. Nothing too tough. I usually let them help decide what they want to do each day. We always have fun, music going... party atmosphere and they all love it. Ages 9-12 are really interesting... they want to work, but you need to keep it fun or you'll lose them down the road. They're just kids.
Good luck!