Does the functionalism view of sociology assume that institutions are intentionally designed to serve their functions?
Since there have been no answers in five days, perhaps I can give a partial answer. I am by no means an expert, so I hope someone will point out my mistakes or if there is any bias (which I am sure there is). Also, my knowledge is limited to political science, but still I hope there is something that you can get from this.
In Britannica, structural functionalism, is defined as &quot;a school of thought according to which each of the institutions, relationships, roles, and norms that together constitute a society serves a purpose, and each is indispensable for the continued existence of the others and of society as a whole.&quot; So for Britannica, the view seems to be about mutually interdependent structures in society. According to wikipedia, a common analogy likens these structures to &quot;organs.&quot; The wikipedia article also lists a lot of criticism to this approach. To give an example of &quot;real research&quot; along these lines; many view the Varieties of Capitalism-framework (Soskice &amp; Hall, 2001) as functionalistic (but you should make up your own mind about that, of course ;)).
A common critique of structural-functionalism is indeed that it explains the existence of institutional arrangements based on some notion of efficiency or optimality. This critique seems to be very common among historical-institutionalists in political science, who stress that institutions are the products of historical processes, and even in cases where they are the products of some group of actors to solve a particular problem, they can often &quot;outlive&quot; their creators and, with time, change to serve entirely new purposes.
An example of this can be found in Kathleen Thelen's critique of the structural-functionalist perspective. In her book How Institutions Evolve (2004), she describes (among other things) how the German system of vocational training evolved from being a system initially designed to weaken the position of the labor movement, to the diametrically opposite position of being a central pillar in the cooperation between the state, employer associations and labor. I recommend reading the introduction and following the references therein - she also references research using the functionalist perspective!
Pierson (Politics in Time, 2004) defines a &quot;functional interpretation&quot; as a view where &quot;institutional arrangements are explained by their outcomes,&quot; or where &quot;institutions take the form they do because powerful actors engaged in rational, strategic behavior are seeking to produce the outcomes observed.&quot; This he calls &quot;actor-centered functionalism,&quot; which he distinguishes from &quot;societal functionalism,&quot; in which institutions exists because they fulfill a certain function for society as a whole.
For Pierson, functional accounts are seen as inadequate for historical research, as they are unable to account for &quot;lag&quot; between the moves of actors and actual institutional outcomes (among other things). I recommend reading Piersons introduction and chapter 4 and 5 if you are interested in what he says about functionalism (I really recommend the entire book, actually :)).
As for my subjective view (for whatever its worth to you ...), I'm not really sure what functionalism really is. I have read many articles that analyze institutions or human behavior using game-theoretic models and so on, and in my (narrow) view, this literature represents the stereotype of functionalist accounts. Even so, there are works that utilize game-theory in historical research (see especially: Greif, Avner, 2006, Institutions and the Path to the Modern Economy) and that tries actively to overcome the sort of criticism that I have cited above, so there is certainly a blurry line of demarcation here.

I am sorry for the heavily biased reply to your post, and I am not entirely sure it was the answer you were looking for. Reading the critique of researchers in the &quot;historical institutionalism&quot; camp will certainly answer your question positively - functionalism is indeed about purposefully designed institutions (but, as Pierson points out, this does not mean that the perspective is without merit!).
Moreover, due to my own narrow perspective; what researchers subscribing to functionalist views themselves think, I do not know. Also, if there is any difference between sociology and political science I cannot tell. Hopefully someone will reply with a more informed view if they feel this reply is inadequate :)