Experimental methods have played a significant role in the growth of English teaching and learning studies. The paper presented here outlines basic features of experimental design, including the manipulation of independent variables, the role and practicality of randomised controlled trials (RCTs) in educational research, and alternative methods and techniques available in the absence of RCTs. It further reviews validity issues inherent in conducting experimental research, in particular sources of internal and external invalidity, and how to remedy them. Along the way, the author suggests that researchers remain mindful of these threats, and calls for the replication of studies across different research contexts with the purposes of the cross-validation and generalisation of findings. The remainder of the paper concludes with suggestions on how to develop a more embedded and sophisticated experimental design in light of the current literature of mixed methodology (Creswell & Plano Clark, 2011), in order to have more explanatory power and compensate for the weaknesses associated with the experimental method. Throughout the paper, the author illustrates the points with examples relevant to English teaching and learning research.