This paper examines longitudinal speech data from two Korean sisters, focusing on English irregular past tense forms to probe the course of attrition within the framework of the regression hypothesis, which suggests that language is lost in the reverse order of acquisition. During the course of attrition, evidence supporting one of the two irregular past tense acquisition theories (blocking vs competition hypothesis) is manifested.

The loss of English past tense forms of two girls who had lived in Anglophone Hawaii for two years before returning to Korea is tracked using free speech samples.

The children’s naturalistic speech data collected over a three-year period after their return is analyzed in terms of accuracy and error types.

Although the older sister did not exhibit clear signs of attrition, the constitution of the younger sibling’s licit and illicit past tense usage varied every year, reflecting her declining proficiency. The results also show that the path of attrition follows the prediction of the regression hypothesis.

The prolonged attrition process of the sisters’ language use, which is unlike acquisition that can happen at a quick rate, demonstrated a relatively large window to witness their reshaping grammar at different interlanguage stages.

The sisters’ irregular past forms retreating to a more rudimentary form provided an opportunity to support the competition model of irregular past tense acquisition. Their past tense accuracy and error analysis demonstrated various past tense forms in competition that could produce a different winner over different periods of time.