We study persistence in one-dimensional ferromagnetic and antiferromagnetic
nearest-neighbor Ising models with parallel dynamics. The probability P(t)
that a given spin has not flipped up to time t, when the system evolves fr
om an initial random configuration, decays as P(t)similar to1/t(theta p) wi
th theta (p) similar or equal to 0.75 numerically. A mapping to the dynamic
s of two decoupled A + A --> 0 models yields theta (p) = 3/4 exactly. A fin
ite size scaling analysis clarifies the nature of dynamical scaling in the
distribution of persistent sites obtained under this dynamics.