Research has found that language development and acquisition occurs in predictable stages for both first/native languages and second (additional) languages. Knowledge of first language learning and acquisition can help teachers better understand the processes that occur when learning a second (or more) languages and recognize what students can be expected to do with the social and academic language they are learning in the classroom.
First Language Acquisition begins from birth and continues through the age of 5. The Sketch Notes below show the stages of First Language Acquisition and characteristics of each stage.
Second Language Acquisition is not defined by age, but can be viewed as beginning once an individual (adult or child) has acquired their first/native language as defined in the stages described above. Just like First Language Acquisition, Second Language Acquisition has been found to move through stages, each with their own characteristics. The infographic below explains the stages of Second Language Acquisition, expectations of what students can do with their language, and "teacher moves" that can be used to help encourage language production from students.
The chart below compares the stages and characteristics of First and Second Language Acquisition. This may be beneficial for lower elementary teachers (K-3) given that along with beginning English acquisition, many lower elementary students are still progressing through the later stages of their First Language Acquisition.
Source: Cirrus Praxis English to Speakers of Other Languages 5352 Study Guide 2018-2019 (Pg 43-51)