Create a third table, named LessonSchedule, with columns:

HorseID $-$ integer with range $0$ to $65$ thousand, not NULL, foreign key references Horse$($ID$)$

StudentID $-$ integer with range $0$ to $65$ thousand, foreign key references Student$($ID$)$

LessonDateTime $-$ date$/$time$,$ not NULL

Primary key is $($HorseID$,$ LessonDateTime$)$