20. A computer processing system programmed to undertake method acts for text passage difficulty estimation, the method acts including: generating, using a computer processing system, an informational text scoring model, wherein generating the informational text scoring model includes: identifying a plurality of texts from a corpus of texts that are informational texts; determining one or more metrics for the informational texts; and configuring the informational text scoring model using the one or more informational text metrics for application in scoring a difficulty of a text passage; and generating, using a computer processing system, a literary text scoring model, wherein generating the literary text scoring model includes: identifying a plurality of texts from the corpus of texts that are literary texts; determining one or more metrics for the literary texts, wherein the literary text metrics include one or more metrics that are not included in the informational text metrics; and configuring the literary text scoring model using the one or more literary text metrics for application in scoring the difficulty of the text passage, wherein the informational text scoring model and the literary text scoring model are configured to provide data about the difficulty of the text passage in a hierarchically structured format.
20. A computer processing system programmed to undertake method acts for text passage difficulty estimation, the method acts including: generating, using a computer processing system, an informational text scoring model, wherein generating the informational text scoring model includes: identifying a plurality of texts from a corpus of texts that are informational texts; determining one or more metrics for the informational texts; and configuring the informational text scoring model using the one or more informational text metrics for application in scoring a difficulty of a text passage; and generating, using a computer processing system, a literary text scoring model, wherein generating the literary text scoring model includes: identifying a plurality of texts from the corpus of texts that are literary texts; determining one or more metrics for the literary texts, wherein the literary text metrics include one or more metrics that are not included in the informational text metrics; and configuring the literary text scoring model using the one or more literary text metrics for application in scoring the difficulty of the text passage, wherein the informational text scoring model and the literary text scoring model are configured to provide data about the difficulty of the text passage in a hierarchically structured format. 24. The system of claim 20 , wherein semantic difficulty is determined based upon word length, word familiarity, word frequency, and rare word frequency.