In the paper, we examine whether and the extent to which CALL grammar instruction contributes to improving learners' performance and confidence in positioning adverbs in an English sentence. Over a two-week period two groups of ESL learners were exposed to six hours of grammar instruction. One group had teacher-fronted instruction while the other was exposed to CALL software. Both groups completed identical tasks in terms of format, instruction, task features, content and feedback. The groups were given a pretest, an immediate posttest, and a delayed posttest. Results showed a significant improvement on the intuition task and a significant confidence improvement on both intuition and production tasks for the computer group. The in-class and the control group showed no significant gains. It is hypothesized that frequency of exposure and practice accounted for the difference between the in-class and the computer group. It is also recognized that students' control of learning, availability of immediate feedback, and non-existence of negative psychological effect that can follow face-to-face negative feedback also contributed to the difference that was found.