Does social interaction increase intelligence? Unless I am mistaken, I recall hearing an English teacher say that social interaction can increase IQ, but I found no sources discussing this when I searched on Google and Google Scholar for it. So, can social interaction increase IQ or intelligence?
NB: my apologies, not enough rep points to post additional links.

this is far too nebulous a statement, and if it were true, would most likely be based on non-experimental data. one example that immediately comes to mind is case studies looking at the effects of social deprivation amongst children in romanian orphanages. there are also a lot of different ways to interpret this question.

for example, is it possible that your teacher was actually referring to vygotsky's  zone of proximal development -- a theory of childhood learning, wherein learning is thought to occur best when interacting with an older, slightly more competent peer? 

in animal behavioural models involving rodents and the like, there is robust empirical evidence that social deprivation is associated with cognitive deficits. 

some examples:


Social isolation rearing-induced impairment of the hippocampal neurogenesis is associated with deficits in spatial memory and emotion-related behaviors in juvenile mice.
Long-term social isolation exacerbates the impairment of spatial working memory in APP/PS1 transgenic mice. 


when looking at animal models one caveat, amongst many, however, is obviously the presumption that we are modelling the same phenomenon in animals as we are in humans. in this case, it certainly looks like social deprivation studies might give us a clue about the effect of social interaction in humans. but could this be modelling something else, say, environmental deprivation? in other words, is there something intrinsically important about social interaction, or is it a form of environmental enrichment, one whose contribution could be supplanted if one were to be exposed to alternative stimuli. but i digress.


  but I found no sources discussing this when I searched on Google and Google Scholar for it. 


rather than social interaction and intelligence, searching for the keywords social deprivation and social isolation may prove more fruitful. instead of IQ, you should use some of the purported factors of IQ, such as working memory. but generally, you will likely find more data on animal behavioural studies than humans.

one exception to this may be the effect of social interaction and acquisition upon language ability, particularly foreign languages. in these domains, you will likely find more robust evidence to support the importance of social interaction:


Foreign-language experience in infancy: Effects of short-term exposure and social interaction on phonetic learning.



  So, can social interaction increase IQ or intelligence?


the cliff's notes of it: 


i think you could confidently say that social deprivation has deleterious effects on cognitive ability.
social interaction is significant in the development of language development, perhaps also verbal ability.
social deprivation notwithstanding, its contribution in a normative population is unclear.