Assign a horse to each lesson slot you want Julia to use. A release-week player learned that adding a horse once did not fill multiple slots. If you want the same horse to do two lessons, put it in two separate slots.
Choose a horse for each lesson
Open Julia's lesson assignments and review the slots one at a time. Pick a horse for each lesson you want to schedule. Use the slot display to check whether the same horse appears where you intended.
Repeat an assignment when it suits the horse
Community reports describe assigning the same horse in several slots. Try filling two slots first and check the resulting workload before adding more. Leave room in the schedule for the horse's other activities.
Review the schedule when work changes
If Julia completes fewer lessons than expected, compare the actual assignments with your plan. A horse entered once may only be scheduled for one lesson. See the Steam discussion on Julia's lesson assignments for the release-week example.
FAQ
Can one horse do more than one lesson with Julia?
Players report that it can when you assign it separately to each intended slot.
Does one assignment fill all remaining slots?
Assign each slot individually. The release-week player reported only one lesson after assigning a horse once.
How should I test a schedule?
Start with a few explicit assignments and compare the completed lessons with the slots you filled.