persons. Order of acquisition In sequential bilingualism, learners receive literacy instruction in their native language until they acquire a "threshold" literacy proficiency. Some researchers use age three as the age when a child has basic communicative competence in their first language (Kessler, 1984). Children may go through a process of sequential acquisition if they migrate at a young age to a country where a different language is spoken, or if the child exclusively speaks his or her heritage language at home until he/she is immersed in a school setting where instruction is offered in a different language. In simultaneous bilingualism, the native language and the community language are simultaneously taught. The advantage is literacy in two languages as the outcome. However, the teacher must be well-versed in both languages and also in techniques for teaching a second language. The phases children go through during sequential acquisition are less linear than for simultaneous acquisition and can vary greatly among children. Sequential acquisition is a more complex and lengthier process, although there is no indication that non-language-delayed children end up less proficient than simultaneous bilinguals, so long as they receive adequate input in both languages. A coordinate model posits that equal time should be spent in separate instruction of the native language and the community language. The native language class, however, focuses on basic literacy while the community language class focuses on listening and speaking skills. Being bilingual does not necessarily mean that one can speak, for example, English and French. Outcomes Research has found that the development of competence in the native language serves as a foundation of proficiency that can be transposed to the second language – the common underlying proficiency hypothesis. Cummins' work sought to overcome the perception propagated in the 1960s that learning two languages made for two competing aims. The belief was that the two languages were mutually exclusive and that learning a second required unlearning elements and dynamics of the first to accommodate the second. The evidence for this perspective relied on the fact that some errors in acquiring the second language were related to the rules of the first language. Another new development that has influenced the linguistic argument for bilingual literacy is the length of time necessary to acquire the second language. While previously children were believed to have the ability to learn a language within a year, today researchers believe that within and