This paper examines the acquisition of verbal morphology in the developing interlanguage systems of Croatian learners of English as a foreign language (EFL). The longitudinal study inquired into the acquisition of four verb tenses (the Simple Present Tense, the Present Continuous Tense, the Simple Past Tense and the Present Perfect Tense) among the same group of 20 elementary school learners over a three-year period of learning (Grade 6, Grade 7 and Grade 8). The acquisition of verb tenses was studied with special empahasis on the second principle of tense-aspect acquisition, i.e. overgeneralization (Bardovi-Harlig 2000). The use of each verb tense was thus investigated exploring the distribution of its overgeneralized use in the environments of other tenses under study. The research was conducted on a corpus of 36 transcribed audiotape recordings of parts of classroom dialogue. The average length of each recording was 15 minutes.