Manipulating the morphology of epitaxial films through detailed control of the growth kinetics has attracted much interest recently. A primary goal is the layer-by-layer growth of smooth films with abrupt interfaces. The most widely used techniques for monitoring the growth mode are diffraction techniques [1 ‐4], where the occurrence of intensity oscillations provides unique evidence for the desired two-dimensional (2D) growth. These oscillations in the diffracted or specularly reflected intensity reflect the periodically varying step density of homogeneously nucleating and successively coalescing 2D islands. The presence of substrate steps can suppress the homogeneous nucleation on terraces in favor of heterogeneous step nucleation still permitting smooth two-dimensional growth. Binding energies for adatoms at step sites are in general larger than on terrace sites due to the increased coordination. As a consequence 2D islands preferentially nucleate at steps if the average adatom diffusion length is larger than the terrace width [5 ‐ 7]. In the submonolayer range this can be exploited to grow quasi-one-dimensional systems like quantum wires using substrate step arrays as a template [8,9]. Similar to the growth mode classification in thin film epitaxy different step decoration modes can be distinguished, the occurrence of which depend on the detailed interaction of the adsorbate with the substrate step [10]. In the present Letter we demonstrate that the step decoration modes can be studied by specular thermal energy helium scattering at grazing incidence. For a regularly stepped Pt(997) surface we find during the adsorption of rare gases and during the deposition of metals in the submonolayer range oscillations in the reflected helium intensity. These intensity oscillations reflect the sequential growth of rows at the steps (named here discrete row growth or row-by-row growth) during deposition.