^^This.
Some other tips:
1. Skills, skills, skills. Skill acquisition needs to be the focus of their junior years. Pedalling circles, bunch skills, braking, cornering, holding a wheel, laying off the wheel, bumping, sliding, emergency braking, eating and dressing whilst riding, etc. Their adolescent physical development will be all over the place, whereas skill acquisition is something you can plan, take control of and measure success in.
2. If you're writing programs, tell them they'll get the next one only after giving you feedback on what they've accomplished (otherwise, what is the point of having a coach?) Also, you may write the most beautifully ornate and effective training programs the world has ever seen, but unless the athlete is engaged with it, it will be meaningless.
3. Plan your sessions so that the athletes know what the goal of the activity is before they show up, how your session fits in with the weekly plan and why it's done in that part of the season.
4. When they show up to training or racing, they should know how to warm up correctly without your input. You are basically teaching them to be independent - you wont be coaching them forever.
5. Skills session need to conclude before they get tired. Keep a close eye on fatigue unless you enjoy strapping broken wrists (I've learnt this the hard way). If they say "But just one more pump track run..." say no. Someone has to be the adult, and that person is you.
6. You can't want something more than they do. It has to come from them
7. Praise the effort and application, not the result. By all means describe the result, but reward their engagement and attitude.
Background: I'm a school teacher but also coached an elite junior development squad for my federation (Aus) for five years. It impacted my family too much so I had to give it away. Graduates range from 'gone nowhere' to 'Team BMC' via an U/23 World title. You'll get all sorts and you need to give them all the best chance that you can. I still take my school group for rides - I could care less if any of them ever enter a race (although some usually end up racing anyway.) We do 20km xc loops on the beautiful singletrack in the surrounding ranges - that counts as a win in my eyes and theirs.