This dissertation project developed and evaluated a computer-assisted language learning (CALL) tool, PAT GRAM, that provides explicit instruction on grammar patterns. Evaluation of the explicit instruction offered by PAT GRAM adopted Chapelle's (2001) framework of criteria for CALL task appropriateness. Following this framework, evidence was collected to investigate language learning potential, learner fit, meaning focus, and impact qualities of the explicit instruction realized through PAT GRAM. To provide evidence for these qualities, this study employed a case study research design including qualitative and quantitative data. The qualitative data encompassed participants' responses to semi-structured interviews and retrospective verbal protocols focusing on their perceptions of learning process and use of PAT GRAM. The quantitative data consisted of participants' pretest and posttest scores on knowledge of verb patterns, revision of sentences that they constructed using the target grammar patterns, and their responses to Likert-scale questions gauging participants' perceptions of learning experience with PAT GRAM. The results suggest that PAT GRAM holds great potential to provide effective explicit instruction on grammar patterns in the target instructional context. This conclusion was drawn based on all four investigated qualities of PAT GRAM, including language learning potential, learner fit, meaning focus, and impact. The language learning potential quality of the explicit instruction using PAT GRAM was strongly supported by evidence showing improved knowledge of grammar patterns, accuracy of pattern use, attention to patterns, and positive perceptions of learning using PAT GRAM. Also, learners' judgment of the explicit instruction using PAT GRAM as appropriate for their level, many incidences of identifying errors, and successful revisions suggest that the explicit instruction offered by PAT GRAM enjoys a high quality of learner fit. Further, participants' attention to meaning of patterns and construction of meaningful sentences lent support for the meaning focus quality of the explicit instruction provided by PAT GRAM. Finally, participants evaluated the impact quality of PAT GRAM positively and perceived the learning experience with PAT GRAM as awareness-raising, autonomy-facilitating, confidence-building, and motivation-stimulating. The results of this study convincingly demonstrated the usefulness and appropriateness of the explicit instruction using PAT GRAM in the university English for second language (ESL) classroom and yielded valuable implications for research on and instruction in L2 vocabulary learning. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]