Assign a horse to each lesson slot you want Julia to use. Release-week player reports say that putting a horse into one slot gives it one assignment. To schedule that horse again, select it in another slot and check how it handles the extra work.
Fill the slots you intend to use
A player who had assigned two horses expected Julia to divide all available lessons between them. The Steam discussion on Julia’s lesson assignments explains the alternative: choose a horse separately for each lesson you want to schedule.
Keep lessons and training in balance
Consider how much work each horse already has. If your main competition prospect needs a training session, leave it room for that work. Use the slots you can support with suitable horses rather than filling every slot regardless of condition.
Review your staffing workload afterward
Compare the lessons you intended to run with what gets done. Then consider how much training your trainer can cover for those same horses. If lesson work crowds out training, reduce repeat assignments or spread them across more suitable horses.
FAQ
Can I use the same horse twice?
Players report that you can select the same horse separately in each intended slot.
Why did Julia run only one lesson with a horse?
Check whether you assigned it to only one lesson slot.
Should I fill every slot?
Fill the slots your horses can handle alongside their care and training.