A variety of different types of designs are used in single- subject research, but according to Neuman and McCormick (1995), there are some features common to most single- subject designs. These are outlined in Table 1. Riley-Tillman and Burns (2009) have stated that in an educational context, single-subject designs allow educators to make research- based observations and judgments about the effectiveness of interventions. One major limitation of single-subject designs is poor external validity. Generalizability of results can only be obtained by replication with other subjects and in different settings. Simonsen and Little (2011) have offered an excellent and detailed discussion of the different types of single-subject designs, along with potential applications for gifted education.