“…Note. E = experimental, QS = quasi-experimental, SA = stand-alone, P = part of comprehensive instruction, T = teacher, R = researcher, UC = usual classroom, AT = alternative treatment, NA = not available Our analysis suggested that there were six major trends: (a) most of the studies focused on older children in Grade 3 or above; only two studies included young children in kindergarten or Grade 1 (Filippini, 2007;Zoski & Erickson, 2017); also, the majority of research was based on Spanish-speaking L2 English learners in the US; (b) there were more quasi-experimental studies than experimental studies with treatment randomization; (c) eight out of 12 studies implemented morphological instruction as part of a more comprehensive curriculum rather than providing it as a stand-alone treatment; (d) the majority of primary studies reported fidelity and feasibility of morphological instruction; (e) there was great variation in the length of instructional time, ranging from one 45-minute session in total (Zhang et al, 2010) to 72 sessions totaling 3,780 minutes (Kieffer & Lesaux, 2012); and (f) there was no notable trend with regard to the following three features. First, in terms of learners' language backgrounds in the treatment group, half of previous research studies included L2 English learners only, and the other half mixed L2 and L1 English learners.…”