This study examines the selective marking of past tense in the narrative prose of low intermediate-level Indian learners of English as a second language who use Hindi or Urdu as their first language, in order to seek effective classroom strategies to address this learning challenge. It tests the applicability of the existing explanations of selective marking on the past tense use of this group of learners and, finding these explanations inadequate, identifies a more viable explanation, with its source in the learners’ L1. This knowledge is used to formulate an effective instructional approach for the learners’ proper mastery of the English past tense. In finding explanations for performance data in processes quite extraneous to the basic developmental process that monitors SLA, the study is able to contribute to the formulation of a more comprehensive and holistic understanding of SLA.