For most runners, cross country is a test of endurance, not speed. If you can get a boy to the point where he can run, and I do mean run, at close to his best effort for 3 miles, the speed aspect takes care of itself. I usually have the runners do 3-4 x 100 at mile effort after their "recovery" runs. I think that suffices as speed work for runners at distances of 5 k and longer during cross country season. Yes, when I have worked with a runner like Bradley Harkrader, or this year Anguel Tolev, I ask them to work on speed a bit more, say they should run 4-6 x 150 m on a slight downhill with a 3 minute jog between each. The 150s are run accelerating to close to top speed for 50 m, maintain top speed for 50 m, they relax and maintain form with less effort the last 50. The hills make the speed faster. This is neuro-muscular training. The muscles need to "know" how to go fast.
I work with mostly runners who are over 30. However, I have been asked to assist with some HS runners, one girls team and a handful of boys from schools attended by children of the older runners I work with. In Colorado, where I live, there are no dual meets during cross country, everything is an invitational. The season starts the last week of August or the first week of September. With a combination of kids who ran all summer up to 80 miles per week, and kids who are lacing up running shoes for the first time in August, I try to allow for both levels with a goal of having everyone on almost the same training by late September. At that point there is only 3 weeks to Regional Championships. To go to state a runner has to be in the top 15, a team has to be in the top 40% of the full teams to complete the regional race typically there are 12 teams in a region, so top 4 teams go to state. The region the girls team is in also has Rocky Mtn HS and Fort Collins HS both ranked nationally or at least regionally. So the early program is two fold, those who have been running continue to run 1 hr a day during the week, 10 miler one day and long run the other on the weekend. The "newbies" are stressed to develop to thepoint where they can cover 40-50 minutes each day. These are total workout times. Include warm-up and cool-down, but not standing around or stretching time. If they are doing 3 x 1 mile with 2 minutes recovery, some girls that is 3/4s of the workout time, then so be it. Fun is a key ingredient. Fitness and work need to be fun, otherwise they'll all would prefer sitting on the bench at the volleyball games.
Tapering starts with October 1. First the long run and 10 milers are cut back to 40-50 minutes. Then efforts and mileage are cut back during the week. After all they have basically 8 weeks to go from non-running to hopefully qualifying for the state meet. Endurance is the key factor that needs to be developed. So the emphasis is on that. This year Allison Gohl went from 19:36 at state last year to hopefully 18:15 or faster. She has run 18:57 twice, both seconds, once a loss by less than 10 seconds to a gal who has run 17:45 on one of the faster courses in the state, the other beating the defending state champ by over 10 seconds but loosing to a freshman in another classification by over a minute. Regionals are tomorrow, I expect her to run low 18s. Others on the team from last year are 60-90 seconds faster than last year. But the team looks like 6th in the Region (numbers 4&5 are running just under 24:00) unless there is some "inspired" running.
Anguel has the 4th fastest time in the state for his classification. But he has run every week of the season off of 60-75 mile weeks. This week is the first time he will be racing with less than 50 miles in his legs. He should win. I'd rather see him pull that off next Saturday at the state meet. Then he and Allison will likely be training by themselves as they prepare to go to the Footlocker Regional meet the Saturday of Thanksgiving.
Hope that helps, if not let me know.