The assumption of this paper in accordance with the cluster model is that nuclei may be considered to be composed of clusters (single nucleons, H 2, He 3, H 3, He 4, etc.). Comparison of cluster model predictions and experimental level schemes are made for the nuclei Li 7, Be 7, C 12, O 16, F 19 Ne 20, Ca 40 and Sc 43. It is shown that comparisons between the spectra of certain pairs of nuclei are particularly relevant from the viewpoint of the cluster model. Comparisons of the spectra of the following pairs of nuclei are made: N 16, O 17; F 19, Ne 20; K 40, Ca 41; and Sc 43, Ti 44. In addition the cluster model predicts levels of parity different than the ground state. The relative position of these nuclei are compared in nuclei in which the smallest cluster is varied from a single nucleon to larger clusters. This model further predicts that immediately after double closed-shell structures, nuclei with H 3 or He 3 clusters (e.g., F 19) will exhibit a strong decrease in this excitation energy. The negative parity states and first 0+ states in alpha-particle nuclei should decrease with increasing atomic number. These predicted systematics agree with the limited experimental data which are available but suggest the need for considerable additional data to further test the predictions. These results indicate substructures which are often more important than shell-model structures.