The present study investigates the factors underlying the difficulty of anaphor resolution tasks in the Invalsi tests. The tasks are grouped according to their difficulty and a qualitative profile of each group has been developed, through an analysis of the influence of factors such as the type of antecedent and the type of anaphoric expression. It is argued that the difficulty of anaphor resolution tasks is influenced by the following factors: the salience and conceptual complexity of antecedents; the formal ambiguity of referring expressions. Syntactically and/or semantically salient antecedents are retrieved more easily than antecedents which are syntactically and/or semantically less prominent. Pronoun resolution tasks, where the surface form of the pronoun does not provide enough information for the identification of the antecedent (e.g. sentences with two possible antecedents of the same gender) are more difficult than those where syntactic gender information allows for the univocal identification of the antecedent.