In this paper, the four possible language acquisition models(the Structure Building Model, the Truncation Model, the Underspecification Model, the Linking Mechanism Switching Model) are considered to examine the auxiliary verb errors produced by the young native English speaking children(L1 young children) and the Korean primary students of English. The prefunctional stage analyses such as the Structure Building Model and the Truncation Model have shown the limitations in explaining the examples such as the interpretation of wh-questions without CP, the movement of default Case subjects within VP without TP and the wh-movement in the utterance of L1 young children, and the difficulties in accounting for the auxiliary verb errors in the Korean primary students over 10 years old, The Underspecification Model has also shown the limitations in explaining the auxiliary verb be insertion errors appearing in Korean primary students’ writings, but not in L1 young children utterance. As a last resort, under the Linking Mechanism Switching Model, it is argued that, unlike English, the syntactic feature checking and agreement in Korean are operated by Merge and Binding rather than Agree and Move. Thus, both L1 young children and Korean primary students have the same syntactic structures based on UG, but the different linking mechanisms of their first languages affect to some extent the process of acquiring English as a first or foreign language. This analysis makes it possible to explain not only the auxiliary verb be insertion errors appearing only in Korean primary students’ writings, but also the similar auxiliary verb errors between L1 young children and Korean primary students. This theoretical study of the auxiliary verb errors needs more experimental studies based on empirical data. However, this theoretical approach is expected to be of a great help in understanding the syntactic processing used by L1 learners and L2 learners.