This study tests the Competing Systems Hypothesis (CSH) as applied to adult second language acquisition of aspect in Spanish. The CSH purports that differences among tutored and untutored learners result from competition between one system of underlying grammatical knowledge and another of learned metalinguistic knowledge in tutored learners (TLs). Twenty-nine first language (L1) English and second language (L2) Spanish (L1-English-L2-Spanish) TLs and 29 native Spanish speakers completed three tasks examining knowledge of Spanish aspect. A Cloze Task targeted typical use of preterit and imperfect morphology, while a Semantic Entailments Task assessed acquired knowledge of entailments falling out from convergence on the aspectual system. Finally, a Binary-Choice Task targeted three pedagogical simplifications common to L1-English-L2-Spanish textbooks: adverbials that 'go with' the preterit or imperfect, 'meaning-changing' verbs in preterit, and the lower frequency of stative verbs in preterit. Results align with the CSH in that TLs performed above 80% accuracy on preterit and imperfect items in the Cloze Task, indicating acquisition of Spanish aspectual morphology. The Semantic Entailments Task further shows TLs converge on underlying knowledge of grammatical aspect by making a significant distinction between logical and illogical entailments. Finally, competition between the underlying grammatical system and learned metalinguistic knowledge is evidenced in the Binary-Choice Task where TLs are less accurate with preterit; specifically, TLs demonstrate effects from pedagogical simplifications regarding adverbials and 'meaning-changing' verbs.