There is one broad distinction that is most fundamental in this context -- the distinction between the construction that happens in the formation of knowledge and that which occurs in the social process involving self- and other-representing agents. The distinction is one between the observer and the observed, and it is not absolute. Participants are themselves knowledge producers, and what we will recognize as their social construction involves their creation of schemes of representation. Nonetheless, there is an important line to draw between the constructions of the observer and the participant.
The crux of the issue is whether social reality is the creation of the men and women who make it up, or whether the reality is shaped and created by the conceptual lenses through which the observer frames the social phenomena. As a social realist, I want to maintain the separation between the social reality as constituted and experienced by the actors and the conceptual schemes of the observer. This position implies rejection of the epistemological version of social constructivism, the view that the observer's concepts determine social reality.
There is a complication that needs to be addressed but that doesn't change the basic perspective of realism. This is the point that in some unusual circumstances it is the case that scientific concepts and theories feed back into behavior and thought of participants. The definition of some mental illnesses is a good example, as is the form of a variety of human institutions such as the factory or the prison: concepts constructed by social theorists and critics feed back into the design of the institution with the result that the next iteration of the institution is indeed partially the construction if the theorist. But these are exceptions, not the rule.
So in what sense are gender, race, or technology instances of social construction from a realist perspective? It is a social reality that societies embody identities for various groups of individuals and these identities are framed by the thoughts, behavioral, and strategies of people in society. Moreover, these thoughts and behaviors change over time as a result of the contestation that occurs around the identities. So the formulation of the identity of "African-American professional," "Jewish garment worker," or "gay Texan" is ultimately the result of a process of contestation, repression, and interactive social behavior. It is socially constructed through visible social processes and mechanisms. And it is constructed, not by the external observer, but by the active and subjective participants.
And what about technology? In what sense is the evolution of a technology like the bicycle or automobile socially constructed? (Of Bicycles, Bakelites, and Bulbs: Toward a Theory of Sociotechnical Change) What historians of technology usually mean by this assertion is a denial of the idea that there is an inherent pathway of technology change that is implied by efficiency and the natural properties of materials and designs. Against this inevitable-ism of function, historians note that the actual path of technology development is most commonly driven or constrained by cultural preferences and expectations. Young men wanted an exciting adventure in their automobile in the 1910s -- and so the boring electric car was doomed (Gijs Mom, The Electric Vehicle: Technology and Expectations in the Automobile Age). Weapons designers shared a culture of precision -- and so inertial navigation superceded radio-guided systems (the predecessor of GPS) (Donald Mackenzie, Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance). In other words -- technologies are socially constructed by the imperatives of culture in the surrounding society.
So there is a sense in which social constructivism is true and informative -- and thoroughly consistent with social realism. And there is another sense in which the phrase is extreme, philosophical, and inconsistent with an empirical and realist study of social reality.(Ian Hacking has an interesting take on these issues in The Social Construction of What?.)