If yours is Bactually a 5-element array of cells, where each element is a 1 by 5 matrix (in fact, each element can contain anything), then
[A.attendance] = B{:}
. 5 5 B :
B_cell = mat2cell(B, ones(size(B,1),1),size(B,2))
temp deal:
[A.attendance] = deal(mat2cell(B, ones(size(B,1),1),size(B,1)))