Once an individual has learned a language fluently, they will be heavily influenced by the grammatical rules and pronunciations of the first language they learned, while learning a new language.

An emerging effective way of measuring the proficiency of a heritage speaker is by speech rate. A study of gender restructuring in heritage Russian showed that heritage speakers fell into two groups: those who maintained the three-gender system and those who radically reanalyzed the system as a two-gender system. The heritage speakers who reanalyzed