Hey coach will give you my view for what it is worth. I am a private coach in Australia. My training group includes at times up to 40 runners both young and old. Here are a few successes: 21 year old new to running ran 49.5 and 1:55 for 4/8 after 6 months of training, 16 year old ran 1:55/4:02 and 18 year old ran 1:54/3:51. I also had a 15 year old boy run 16:07 for 5k on track off 40k per week. We only do 1 track session per week.
Our standard week during prep for track season
Monday easy run 30-40 minutes
Tuesday 1600/2k threshold 3 min recovery 2x4x400 at 3k/5k pace on 2 min cycle 3 min between sets
finish w/3x200 or 150 with lots of recovery
Wednesday 40-60 minutes of easy running (3:51 1500m runner regularly runs 7:30-8 min miles for this)
Thursday 6x3min at 5k/8kpace with 90 seconds rest 3 min rest 5x100m with 100 walk all on grass
Friday OFF
Saturday this varies sometimes 10k progressive which starts off at 5 min k pace and goes down to 3:20/15 pace or hilly 9-12k circuit surging hills which includes 2x900 and 1x700m hills
Sunday easy 50-60 minutes
We are also big into alternations which when they are recovering it is more of a float. We sometimes do this over 800-1200 meters ex 1k repeats as 400 at 3-5k pace with 200 in 45 followed by another 400 at 3-5k pace.
For your shorter distance runners have them regularly do 150's or flying 80's to work on speed. We also do short hill repeats regularly throughout the season. Ex 8x 6 second or 10 100m after this we do solid run of 2.5 to 5k depending on athletes.
Good luck