An evaluation measure (EM) guides a learner's choice of grammar when more than one is compatible with available input. EM must be universal, so children receiving comparable input acquire comparable grammars. It must favor the choices children actually make. The theoretical shift from rule-based grammars to principles-and-parameter-based grammars…

This article suggests a method to deal with cross-linguistic differences in children with Specific Language Impairment. The differences in vulnerable structures reflect typological properties of the surrounding language (e.g., Leonard 2014a, 2014b). This article adds a developmental perspective to the discussion by interpreting the vulnerable…