Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for grouping of users. In one aspect, a method includes selecting a current user group for a search session based on search results selected by a user during the search session. The method also includes obtaining a plurality of search results responsive to a query submitted by the user during the search session wherein each of the search results has a respective score. The method also includes determining that a search result in the plurality of search results is one in which users associated with the current user group select as a selected search result a percentage of time more often or less often than a general population of users that is larger than a number of users associated with the current user group. The method also includes in response to determining, modifying an order of the plurality of search results by modifying the respective score of the search result based on the percentage. The method also includes providing the modified plurality of search results in response to the query.