The n-dimensional affine
group over GF(2) is triply transitive on 2n symbols. For n ≧ 4,4 ≦ k ≦ 2n−1, any
orbit of k-subsets is a 3 − (2n,k,λ) design. In this paper a sufficient condition that
such a design be a 4-design is given. It is also shown that such a 4-design must always
be a 5-design. A 5-design on 256 varieties with block size 24 is constructed in this
fashion.