We consider Sch\"odinger operators on the half-line, both discrete and
continuous, and show that the absence of bound states implies the absence of
embedded singular spectrum. More precisely, in the discrete case we prove that
if $\Delta + V$ has no spectrum outside of the interval $[-2,2]$, then it has
purely absolutely continuous spectrum. In the continuum case we show that if
both $-\Delta + V$ and $-\Delta - V$ have no spectrum outside $[0,\infty)$,
then both operators are purely absolutely continuous. These results extend to
operators with finitely many bound states.