You can use School and Year field values as group and use current session rank as condition to lookup the previous records.
[School] = EARLIER ( Table[School] )
&& [Year] = EARLIER ( Table[Year] )
&& [Sesion Rank]
= EARLIER ( Table[Sesion Rank] ) - 1
) + 0
Community Support Team _ Xiaoxin
If this post helps, please consider accept as solution to help other members find it more quickly.