“…This confound is problematic because spacing usually boosts subsequent test performance—indeed, this spacing effect is one of the most robust effects in the area of learning (for reviews, see, for example, Cepeda, Pashler, Vul, Wixted, & Rohrer, 2006; Dempster, 1987; Bjork, 1994; Donovan & Radosevich, 1999; Rohrer, 2009; for experimental papers, see, for example, Bahrick, H. P., Bahrick, L. E., Bahrick, A. S., & Bahrick, P. E., 1993; Bloom & Shuell, 1981; Cepeda, Vul, Rohrer, Wixted, & Pashler, 2008; Cook, 1934; Kornell & Bjork, 2008; Lee & Genovese, 1988; Mumford et al, 1994; Pyc & Rawson, 2007; Rea & Modigliani, 1985; Rohrer & Taylor, 2006; Seabrook, Brown, & Solity, 2005).…”