1. A computer-implemented method comprising: determining, by a data processing apparatus, that at least two or more previous search queries, previously received from a particular user device, are search queries for a same topic; determining that the particular user device requested presentation of fewer than a specified number of web pages referenced by search results provided to the particular user device in response to the previous search queries; identifying, in response to determining that both the two or more previous search queries are related to the same topic and that fewer than the specified number of web pages referenced by the search results were requested, a related query for the same topic as the two or more previous search queries, the related query being different than each of the previous search queries; receiving, by a data processing apparatus, a current search query from the particular user device, the current search query being received subsequent to the two or more previous search queries; and providing, for presentation on a search results page for the current query, the identified related query to the particular user device.